The invention discloses an on-car revolution energy-saving system comprising a multiway valve, an on-car revolution device, an operation detection signal generator, a controller, a control block, a main pump and corresponding connections. With the adoption of the on-car revolution energy-saving system, oil overflow can be effectively prevented during on-car revolution starting, system heat generation can be reduced, and the purposes of reducing energy consumption of a prime motor, saving energy and improving work efficiency can be also achieved.