The invention relates to a crankcase ventilation system of a supercharged gasoline engine and a work method of the crankcase ventilation system. Crankcase waste gas in a low-load state passes through a valve cover (4), a three-way pipe (6), a PCV (positive crankcase ventilation) valve (9), an air inlet manifold (7) and a combustion chamber in sequence; an air supply channel (17) is formed between an air inlet hose (14) and a crankcase; an air supply channel one-way valve (16) is arranged on the air supply channel (17); supplied fresh air passes through the air inlet hose (14), the air supply channel (16), the air supply channel one-way valve (16), the crankcase, an air cylinder body (2) and the valve cover (4) in sequence; generated waste gas passes through the same path as the crankcase waste gas. According to the crankcase ventilation system, the one-way valve is opened to supply the fresh air to the crankcase by the characteristic that the negative crankcase pressure value in the low-load supercharged gasoline engine is excessively high, so that on one hand, an effect of adjusting the crankcase pressure is achieved, and on the other hand, the supplied fresh air has the effects of scavenging and purifying the crankcase waste gas.