To further improve the output power of the multi-single emitters diode laser, based on the analysis of the common stepped multi-single emitters diode laser array, this paper proposes to fill the beam in the slow axis direction with small spot size, and under the same coupling condition, more laser energy is coupled into the fiber to achieve higher power output. The beam-parameter product is used as the index to evaluate the beam quality, and the feasibility of slow axis beam filling is demonstrated. By using ZEMAX simulation software, the comparison simulation of 8-way ladder type multi-single emitters diode laser array and 12-way filling array is carried out. On the premise of not affecting the coupling efficiency, the 12 single emitters diode laser with center wavelength of 860 nm and output power of 3 W is coupled into a fiber with core diameter of 105 um and numerical aperture of 0.22, the output power is 33.4 W and the coupling efficiency is 92.78%. The simulation results show that the slow axis beam filling can improve the power output of the diode laser to a certain extent.