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.