In order to reduce size effect error of accelerometers caused by single-axial rotation of the single-axial rotation of INS (SRINS), the size effect error of accelerometers caused by the rotation was analyzed, the error of velocity caused by the size effect error of accelerometers was researched, and the compensation method was offered. According to theory analysis and simulation results, the size effect error could not bring on emanation of positioning error, however, it would increase surge of velocity errors, for the damping system, it would bring on bigger velocity errors: The precision was improved in the rotating process by compensating the size effect errors.