The invention discloses an electromagnetic variable 
cam mechanism and a small-fluctuation variable-flow 
oil supply device. The small-fluctuation variable-flow 
oil supply device comprises an 
oil tank and an 
oil pump, wherein the 
oil pump is composed of a cylinder body and a 
piston, an oil inlet of the cylinder body is communicated with the 
oil tank through an oil 
inlet valve and a filter, an oil outlet of the cylinder body is communicated with an oil inlet of an electric-control oil 
injector through an oil outlet valve and a 
pressure sensor, an oil return port of the electric-control oil 
injector is connected with an oil return port of the 
oil tank through an oil return control valve, the lower end of the 
piston makes contact with a single-action 
cam or a multi-action 
cam, and the 
pressure sensor, the electric-control oil 
injector, an 
electromagnetic coil and the oil return control valve are connected with a power source and a controller. According to the small-fluctuation variable-flow 
oil supply device, the single-action cam or the multi-action cam is selected to be used for changing the oil supply capacity of the 
oil pump in real time according to the rotating speed working condition and the load working condition of an engine, the amount of returned oil is controlled through the oil return control valve, the amount of returned oil of the oil pump is reduced, and 
fuel oil supplying efficiency is improved.