A non-mechanical beam steering system is proposed and designed to resolve the problem of approaching the far-field diffractive pattern with laser beams. A beam steering method based on the phase only modulation with a liquid crystal spatial light modulator (LCSLM) is studied and described to control the light beams programmably. The Fourier iterative optimal algorithm is adopted to design the optimal phases approaching the expected far-field diffractive pattern. The schematic diagram and the experimental set-up are given. Results show that the method can generate 2-D spots arrays with the intensity error rate less than 8%. The response time of generating the dynamical diffractive pattern is less than 100 ms. With the merits of lightness, precision and quick response, this scanning system is of value in the fields of multi-object tracing, laser guiding and multi-object defense.