The invention discloses a state machine based diesel engine grid heating control method. A whole heating process is divided into a setting state, a preheating state, a crankshaft heating state, a post-heating state and a closed state. The setting state enters the preheating state after 2 sec delay; an initial start temperature can be calculated in the preheating state according to an intake manifold temperature and a coolant temperature, and the preheating time can be obtained according to a preheating temperature interpolation table through interpolation; the crankshaft heating state can be entered when a rotating speed is higher than 25 RPM, and a fixed time can be effectively maintained by crankshaft heating when the initial start temperature is lower than -1 DEG C and the engine rotating speed is higher than 4200 RPM; the post-heating state can be entered when the rotating speed is higher than 600 RPM, and a post-heating temperature can be calculated according to the temperature; apost-heating plan can be calculated according to the post-heating temperature; a post-heating time can be obtained by a post heating interpolation table through the interpolation according to the post heating plan and a post-heating phase; heating power can be output according to a determined plan; and the closed state can be entered when the post-heating phase ends or start timing sequence ends.