The invention provides a crankcase ventilating system structure which comprises a crankcase, an upper-layer exhaust gas channel and a lower-layer exhaust gas channel, wherein the crankcase is communicated with the lower-layer exhaust gas channel; the lower-layer exhaust gas channel is communicated with the upper-layer exhaust gas channel through a pipeline; the upper-layer exhaust gas channel is communicated with a respirator. The crankcase ventilating system structure has the advantages and positive effects that a double-layer exhaust gas channel structure is adopted, exhaust gas low in oil content directly enters into the upper-layer exhaust gas channel, exhaust gas high in oil content enters into the lower-layer exhaust gas channel, is subjected to once oil-gas separation, then enters into the upper-layer exhaust gas channel through the pipeline and enters into the respirator from the upper-layer exhaust gas channel, the oil content of the exhaust gas entering into the respirator is effectively reduced, and the pressure loss is reduced.