An imaging system is provided. The imaging system comprises a first imaging device and a second gantry. The first imaging device comprises a first gantry, a first X-ray source provided on the first gantry and a first detector that is opposed to the first X-ray source and provided on the first gantry. The first imaging device is used to execute a first imaging mode. The second gantry is separably connected with the first gantry, and executes a second imaging mode combined.