Laser has been widely used in laser medical treatment, radar, laser guidance, welding, and other fields. Many applications require specific modes, and the laser beam mode generated by the laser is usually Gaussian. For these particular cases, beam shaping is indispensable. The Diffractive Optical Element (DOE) is small in size, light in weight, easy to control the wavefront, and has good beam shaping performance. There are many ways to design DOE, such as genetic algorithms, simulated annealing algorithms, geometric algorithms, and iterative Fourier transforms. For optical design, a single algorithm is usually not enough. For example, genetic algorithms have strong global optimization capabilities and weak local optimization capabilities. The global optimization ability of the simulated annealing algorithm depends on the annealing temperature. If the temperature drops too fast, it is easy to skip the minimum value, and if the temperature drops too slow, the optimization time is too long. The iterative Fourier transform algorithm has the advantages of being fast and efficient and is an ideal choice for DOE design, but it is easily affected by the initial stage, leading to poor final results. A single algorithm cannot obtain satisfactory design results due to inherent defects. Some improvements on single algorithms or hybrid algorithms, such as the genetic simulation hybrid algorithm, fuzzy control iterative algorithm, and double-constrained GS improved algorithm, can compensate for the above shortcomings.To improve the efficiency and light quality of the optical diffractive element, an improved GS algorithm is proposed, in which the initial phase is introduced, and an iterative optimization algorithm is employed to obtain the best parameters. The iteration and neighborhood optimization algorithms are adopted to obtain the best DOE phase. The proposed design method can effectively improve the beam quality and diffraction efficiency. The DOE phase-by-phase unwrapping algorithm can generate a continuous surface suitable for diffractive devices manufactured by moving mask technology and reduce the machining errors introduced by quantization. In the simulation results, the diffraction efficiency is 0.999, and the root mean square error is 0.018 7. The experimental speckle contrast is approximately 0.011 8. In addition, the influence of four factors on the quality of the output spot is discussed: 1) The proposed phase parameter has a significant influence on the quality of the output spot, and there is an optimal value that can meet the requirements of high diffraction efficiency and low root mean square error. The simulation results of the light spots with the phase parameter d equal to 40, 62, and 90 are given here. When phase parameter is 40, there is a large bulge in the center of the output point. When phase parameter is 90, the output spot has noticeable depressions; when phase parameter is 62, the quality of the spot is the best, with neither protrusions nor depressions. 2) The waist radius of the incident Gaussian beam is also an important factor affecting the output spot. The simulation results for waist radii of 650 μm, 960 μm, and 1 550 μm are given. When waist adius is 650 μm, the uniformity of the output light spot decreases, and some fringes appear. When waist adius is 1 550 μm, the output light spot has prominent fringes, and the energy of the light spot drops significantly. When waist adius is 960 μm, the output spot uniformity is good, and most energy is concentrated in the target area. There is an optimal positional relationship between the incident Gaussian beam and the DOE. 3) The center of the incident Gaussian beam should be aligned with the center of the DOE. If it deviates from the optimal position relationship, the output light spot will be greatly affected, and the quality of the light spot will be reduced. This paper presents the simulation results of two horizontal directions with center deviations of -1.024 mm, 0 mm, and 1.024 mm. The right direction is defined as the positive direction. It can be seen from the figure that the deviation of the two centers causes streaks in the output light spot, and the uniformity is reduced to a certain extent. 4) Two random disturbances of 0.10π and 0.01π were added to the final DOE phase distribution and compared with the undisturbed results. It was found that the diffraction spot did not change significantly under the random disturbance of 0.01π, which was almost the same as the original spot. Even if a random disturbance of 0.1π is added, the shape of the diffracted spot remains good; only an inevitable decrease in the internal uniformity and speckles appear in the target signal area.