The invention relates to a hybrid electric vehicle and a urea injection control method and system thereof. The urea injection control system in the hybrid electric vehicle comprises a urea pump an outlet of which is used for being communicated with an exhaust pipe, the urea pump is further connected with a gas source used for feeding urea injected out of the urea pump into the exhaust pipe, and anair solenoid valve for controlling the connection and disconnection of a connecting pipeline is installed on the connecting pipeline of the gas source and the urea pump; the urea injection control system of the hybrid electric vehicle further comprises a controller, and the controller is connected with the urea pump and the air solenoid valve separately, controls the urea pump and the air solenoid valve to be switched on when an engine runs and controls the urea pump and the air solenoid valve to be switched off when the engine does not run. Starting and stopping of urea injection are relatedto the working state of the engine, the consumption of urea is greatly reduced through the mode, the high-pressure gas is also saved, the workload of the engine for preparing the high-pressure gas isreduced, and the energy consumption of the whole vehicle is reduced.