In order to improve the orientation accuracy of the rotating GNSS short-baseline dual-antenna/MIMU integrated system, its tight integrated system is constructed in this paper. In the tight integrated algorithm, the pseudorange, pseudorange rate and carrier phase of the GNSS are taken as the observations of the rotating GNSS dual-antenna/MIMU integrated system. The extended Kalman filtering is used for the estimation, and the estimated stat quantity is used for the closed-loop feedback in the system, and finally the orientation result of the integrated system is obtained. The tight integrated off-line calculation of the ship-borne test data of the rotating GNSS dual-antenna/MIMU integrated system is carried out. The results show that when the GNSS baseline is 0.3 m, the heading error of the integrated system is less than 1°, and the pitch and roll angle errors are less than 0.1°.