Abstract: A fabric light transmittance testing device comprises a supporting frame, a middle portion of an inner side of which is fixedly connected with a platform plate, a top surface of the supporting frame is fixedly connected with a top fixing plate having a top surface fixedly connected with a hydraulic rod, a bottom surface of the platform plate is fixedly connected with a light transmission testing mechanism, a cloth fastening mechanism is arranged above the light transmission testing mechanism, one side of the top fixing plate is provided with an unwinding control mechanism, four vertical sliding rods slidably penetrate through an upper surface of the top fixing plate, a bottom surface of the vertical sliding rod is fixedly connected with a detection bottom plate, a top surface of the platform plate is fixedly connected with a slope plate, and the light transmission testing mechanism comprises a side fixing plate.