Calibration error analysis of inertial measurement units (IMU) is significant for evaluating navigation system performance, allotting errors, and choosing devices in projects. However, few researches on IMU calibration give the quantificational forms of calibration errors. Based on quaternion, this paper constructs an error model about axes perpendicularity errors and angle control errors of a turntable. Considering measurement errors of gyroscopes and accelerometers in an IMU, we derive the calibration parameters' errors using a typical multi-position calibration method. Finally simulations and calibration tests of a laser gyro strapdown inertial navigation system are performed to verify the calibration error analysis.