The invention provides a forward scattering visibility meter outdoor calibrating device based on an integrating sphere. The device comprises an integrating sphere, an adjustable diaphragm, a photoelectric detection module, a signal preprocessing unit, an analog-to-digital conversion circuit, a central processing unit, a signal output circuit and an integral sphere bracket. The integrating sphere is installed in the scattered light sampling area of the forward scattering visibility meter, the light entrance hole and the light exit hole of the integrating sphere are designed to point to the transmitting end and the receiving end of the device respectively, and the adjustable aperture is disposed on the light entrance hole of the integrating sphere to simulate the quantitative change of the scattered light, thereby calibrating the intensity of the light source, the sensitivity of a photoelectric detection system, and the accuracy of the system. The device is small in size, simple in structure, easy to install and convenient to operate, and avoids a complicated process of moving the device from an outdoor field to a laboratory for calibration in traditional calibration, and avoids thatrepeated installation may affect the accuracy of a measurement optical path.