To solve the problems of improving retrieved speed accuracy and optimal parameters design in spatial filtering velocimeter (SFV), a weighted average of logarithm of speed retrieval algorithm is researched based on computer simulation. With well designed simulation experiments, the moving targets’ images by a linear COMS image sensor and retrieved speed accuracy are both evaluated. Within the targets’ speed range of 0.1~100m/s, the designed SFV could retrieve targets’ speed correctly. The relative mean speed and standard deviation errors are -0.250% and 0.623%, respectively. The weighted average of logarithm speed retrieval algorithm with different power thresholds is researched as well based on the computer Monte Carlo simulations. The simulation results show that a suitable power threshold in SFV would improve the retrieved speed accuracy. Take a moving target’s speed of 100m/s for example, the retrieved speed accuracy improves from 1.065m/s to 0.381m/s (or relative speed error improves from 1.065% to 0.381%) with the power threshold decreases from 0 dB to -5dB.