In order to realize the beam shaping of high-power diode laser stack by microlens array, the technique of high fill factor diode laser stack slow axis direction beam collimation is researched. The diode laser stack is accompanied with micro-cylindrical-lens of fast axis collimated. The influence of the fill factors in the slow axis direction on collimating space is analyzed. For the diode lasers with the luminescence unit size of 100 μm and the period size of 200 μm, it is difficult to collimate the slow axis direction beam by the use of micro-cylindrical-lens array, besides, there is not enough space for the fast axis beam collimation. In order to remove the influence of fill factor, bar is acted as the collimating unit in the slow axis direction for the high-power diode laser stack with the fill factor of 0.5, and simulation is carried out by the optical design software Zemax. The remaining divergence angle of slow axis direction beam after collimating is tested based on space scanning and achieve the half of the remaining divergence angle of 2.12°. The experimental results show that the collimating way of diode laser slow axis direction beam is effective. The beam collimating way proposed is simple and easy, so it is useful for high fill factor diode laser stack slow axis beam collimation.