In order to solve the problem in the accuracy of circularity of apple, the improved algorithm of the particle swarm was adopted. Firstly, mathematical model circularity of apple was established. Secondly, particle swarm algorithm was improved, which was included inertia weight fuzzy control based on membership function of generalized bell shaped distribution, adaptive Z shaped membership function adjustment process, and selecting fitness function. Finally, the algorithm termination condition and flow were given. The experimental simulation results showed that the improved particle swarm optimization algorithm convergence was faster than the particle swarm optimization, and the accuracy of Jonakin and Fuji Apple roundness detection, about 96% and 97%, was higher than that of other algorithms. In conclusion, this could algorithm be used for circularity of apple measurement.