Aiming at the problem of flow field non-uniformity of the post-mixed abrasive nozzle at present，the FLUENT simulation software is used to calculate the internal flow field of a new type of post-mixed abrasive water jet nozzle. The influence of conical baffle on the uniformity of flow field is analyzed by comparing the internal flow fields with and without conical baffle. By analyzing the spray effect of tapered baffle nozzles with different parameters，the influence rule of different parameter structure of the new-type post-mixed abrasive water jet nozzles on the uniformity of internal flow field is obtained，so as to improve the mixing uniformity of water and abrasive in the post-mixed abrasive water jet nozzles. The results show that air pressure reduces and fluid collection is eliminated in mixing chamber when increasing the diameter of the shrinking outlet on precondition of assuring high outlet velocity. On this basis，the abrasive volume fraction of outlet is nearly 15% with the minimum fluctuation，the abrasive mixing uniformity is greatly improved when a cone baffle structure of quadric B-spline curve is added inside the nozzle and abrasive inlet leans toward axis of the nozzle at the angle of 45°. The effects of multi-parameters on the uniformity of the abrasive were analyzed by orthogonal test to obtain the optimal structural parameters.