A power electronic device cooling system, comprising: an air conditioning unit, a coolant pump , a bypass throttling element and a cooler, wherein the air conditioning unit comprises an evaporator , a compressor, a first condenser and a main branch throttling element which are connected into an air conditioning cooling circulation system, the first condenser , the coolant pump , the bypass throttling element , the cooler and the evaporator are sequentially communicated, an inlet of the coolant pump is communicated with the first condenser , an outlet of the coolant pump is communicated with a first end of the bypass throttling element , a second end of the bypass throttling element is communicated with a first end of the cooler, a second end of the cooler is communicated with the evaporator , and the cooler exchanges heat with a power electronic device to cool the power electronic device; the power electronic device cooling system further comprising a second condenser , wherein the second condenser is connected between the cooler and the evaporator ; the power electronic device cooling system is configured such that when air conditioning unit is started the liquid coolant goes through a coolant circulation pipeline in parallel to the coolant pump , the power electronic device cooling system further comprising a one-way valve , wherein the one-way valve is provided on the coolant circulation pipeline, an inlet of the one-way valve is communicated with the first condenser , and an outlet is communicated with the first end of the bypass throttling element ; when the air conditioning unit is stopped, the coolant pump is started to provide coolant for coolant circulation. an air conditioning unit, a coolant pump , a bypass throttling element and a cooler, wherein the air conditioning unit comprises an evaporator , a compressor, a first condenser and a main branch throttling element which are connected into an air conditioning cooling circulation system, the first condenser , the coolant pump , the bypass throttling element , the cooler and the evaporator are sequentially communicated, an inlet of the coolant pump is communicated with the first condenser , an outlet of the coolant pump is communicated with a first end of the bypass throttling element , a second end of the bypass throttling element is communicated with a first end of the cooler, a second end of the cooler is communicated with the evaporator , and the cooler exchanges heat with a power electronic device to cool the power electronic device; the power electronic device cooling system further comprising a second condenser , wherein the second condenser is connected between the cooler and the evaporator ; the power electronic device cooling system is configured such that when air conditioning unit is started the liquid coolant goes through a coolant circulation pipeline in parallel to the coolant pump , the power electronic device cooling system further comprising a one-way valve , wherein the one-way valve is provided on the coolant circulation pipeline, an inlet of the one-way valve is communicated with the first condenser , and an outlet is communicated with the first end of the bypass throttling element ; when the air conditioning unit is stopped, the coolant pump is started to provide coolant for coolant circulation. <EOS>