Method and device for detecting source image distance

The embodiment of the present invention discloses a method and device for detecting a source image distance (SID) applied to a radiographic imaging device. The radiographic imaging device comprises astructure provided with a radiation source, a beam limiter which is connected to the structure and is used for controlling a radiation angle and a detector which is perpendicular to a radiation direction. When the SID of the radiation imaging device is determined, firstly an opening width of the beam limiter and a zone width of a projection zone on the detector in the width direction of a beam limiter opening can be obtained, and then the SID of the radiographic imaging device can be determined according to the opening width, the zone width and a distance from the radiation source to the beamlimiter opening determined in real time. In the process of detecting the PID, the installation of additional positioning device on the radiographic imaging device is not needed, and the overall designdifficulty and cost of the