An adaptive complementary filtering fusion algorithm is proposed to solve the instability of GPS positioning signal which is often encountered in operation of plant protection unmanned aerial vehicle（ UAV）. The optical flow module is used to modify positioning signal and integration architecture of algorithm is introduced.Stability analysis is carried out in frequency domain. Experiment is designed to verify the validity of the algorithm.The experimental results show that when the GPS signal is very good

the positioning effect is better and the effect of the fusion algorithm is less obvious. When the GPS module is slightly disturbed

the positioning signal drift is relatively serious

positioning effect using the fusion algorithm is improved

at the same time

increase signal redundancy

solve the problem of signal loss.