A method, apparatus and terminal device for synchronous exposure applicable to a primary camera in a multi-camera system is provided. The method includes: after receiving an instruction for synchronous exposure, obtaining a plurality of initial hardware time codes by acquiring an initial hardware time code of each camera in the multi-camera system, determining a synchronization reference value according to the plurality of initial hardware time codes and, based on the synchronization reference value and the initial hardware time code of each camera, determining a frame compensation value corresponding to each camera, and transmitting the frame compensation value of each secondary camera to the corresponding secondary camera, such that when the primary camera adjusts an image length according to the corresponding frame compensation value, each secondary camera adjusts an image length of the image according to the corresponding frame compensation value, to synchronize exposure time of all cameras.