Thrust ripples are the main factors which affect the application and development of permanent magnet linear synchronous motor (PMLSM). In order to control and compensate the thrust fluctuations of permanent magnet synchronous motor, the mathematical model of thrust fluctuations must be established first. In this article, the theoretical analysis and derivation of the main factors affecting thrust ripples such as the disturbance of force ripple, edge effect are done in detail, after that a large number of experiments is carried out to test the thrust ripples, then the spectrum analysis of test data are made to find out the main frequency components and harmonics, last the mathematical model of thrust fluctuations are achieved, which provide the basis and foundation to compensate for thrust fluctuations through the methods of control.