Control method and system for controlling cooling water heater and cooling water heater

The invention discloses a control method for controlling a cooling water heater. The method includes the steps that whether an engine is started normally or not is detected in real time first, and if yes, the environment temperature begins to be detected in real time; when the environment temperature is smaller than or equal to a first preset temperature, the first temperature of a cooling water outlet of the engine begins to be detected in real time; when the first temperature is larger than the first preset temperature and is smaller than or equal to a second preset temperature, the heater is in a full-power working condition; when the first temperature is larger than the second preset temperature and is smaller than or equal to a third preset temperature, the heater is in a power-reduction working condition; and when the first temperature is larger than or equal to the third preset temperature, the heater is in a stopped working condition. By the adoption of the control method, the cooling water heater of the engine operates through a set control method, and thus the warming requirement of the engine can be met. The invention further discloses a system for controlling the cooling water heater and the cooling water heater.