The invention discloses a carbon steel surface strengthening composite nitriding process. The process comprises the steps of compression treatment, micro-machining treatment before nitriding, surfacehigh-frequency quenching treatment before nitriding, micro-machining treatment before nitriding, workpiece boxing, control atmosphere filling and plasma nitriding, wherein the plasma nitriding temperature is 480-500 DEG C, the heat insulation time is 3-4h, and control atmosphere is methane and ammonia gas; workpieces need to be cleaned with diluted hydrochloric acid before nitriding, flushed withethyl alcohol and then blown by an air blower to be dried; after the interior of a furnace is vacuumized to about 10 MPa, the furnace is filled with control atmosphere, the work air pressure is maintained at 100 MPa, and the workpieces are placed into the furnace after the temperature is increased to preset temperature, and cooled along with the furnace after heat insulation. A white compound layer in a nitriding layer is continuous, uniform, compact and combined with a substrate firmly and has the thickness being about 6-15 micrometers, and the process is scientific, reasonable and large in achievement transformation potential.