The invention belongs to the field of field irrigation and fertilizer distribution and discloses a mobile multifunctional constant-pressure irrigation fertilizer distributor and an irrigation and fertilizer distribution method thereof. The irrigation fertilizer distributor comprises a main pipeline, a water pump and a fertilizer applicator. The main pipeline is used for conveying water-fertilizer fixed liquid. The water pump is used for extracting irrigation water of the main pipeline and adjusting water inflow of the irrigation water. The water pump is controlled by a variable frequency constant-pressure control device to pressurize the irrigation water. The fertilizer applicator is used for conveying fertilizer and nutrient solution to the main pipeline. The variable frequency constant-pressure control device is connected with the main pipeline through a pressure sensor and used for receiving pressure signals acquired by the pressure sensor and controlling rotation speed of the water pump. By the irrigation fertilizer distributor and the irrigation and fertilizer distribution method thereof , irrigation pressure and flow can be controlled simultaneously, stable system fertilizer distribution concentration can be guaranteed while blocking and corrosion of the irrigation system can be prevented, the requirements for even and high-quality irrigation and fertilizer distribution can be satisfied, and energy conservation can be achieved.