The invention relates to completely-synthesized heavy-load open industrial gear oil comprises the components: PAO base oil, a low-sulfur and low-phosphorus extreme pressure antiwear additive, a friction improver, a high-temperature antioxidant, a metal deactivator, a viscosity index improver, a pour point depressant and a rust inhibitor, and the PAO base oil is poly-alpha-olefin. The completely-synthesized heavy-load open industrial gear oil provided by the technical scheme is low in friction force and also relatively low in operating temperature and can be used under a severe condition and used for improving the scratch resistance and corrosion resistance. Meanwhile, the completely-synthesized heavy-load open industrial gear oil can be used for reducing exhaust emission and reducing pollution and is environment-friendly.