A stage light fixture with an optical parameter detection function includes a light head, a supporting arm and a case. A light source for generating a light path, a light guiding member for guiding light to deviate from the light path, and an optical parameter detector are provided in the light head. The light guiding member can be freely switched into/out of the light path via a driving mechanism. The optical parameter detector can receive and detect the light guided out by the light guiding member. According to the present invention, the light guiding member can be switched into the light path to guide the light to the optical parameter detector for detection, only when the stage light fixture is started to work, or detection is performed at an interval between operations of the stage light fixture, while switched out of the light path when in operation.