The present invention discloses a plasma sheath curvature measurement method of an ion thruster. The method employs equal plasma density on a sheath curved surface and the plasma density jump at adjacent positions of an ion beam downstream to measure the plasma density so as to find out the sheath curved surface and obtain a sheath curvature. The present invention can provide a method for obtaining a plasma sheath curved surface so as to complete the ion thruster grid system design method and make up the problem that the design of the ion thruster grid system does not consider the plasma sheath curvature influence.