The integrated measurement system of the strapdown inertial navigation system (SINS) and global positioning system (GPS) has become a key technology of airborne earth observation. In order to build an precise error model to improve the estimation accuracy of SINS/GPS integration, especially the attitude estimate accuracy, this paper analyzes the effect of the main part of the inertial measurement unit (IMU) calibration errors on SINS/GPS integration accuracy based on the imitated flight track of airborne earth observation imaging. The results of simulation show that the installation errors of gyro have the most serious effect on the attitude accuracy of SINS/GPS integration, and the gyro Markov process and accelerometer Markov process come second. The investigative results would offer the principle foundations for the design of the precise error model of SINS/GPS integrated measurement system.