The invention relates to a diesel engine starting assistance system and a diesel engine starting assistance method applicable to a high attitude area. The system comprises an auxiliary booster air intake pipe, low-pressure-ratio high-flow fluid machinery, an atmospheric pressure sensor, a cooling fluid temperature sensor and a control unit, wherein an air inlet is connected with the air intake end of a turbine booster air intake pipe and the air intake end of the auxiliary booster air intake pipe respectively through an air shunt valve; the air intake end of an intercooler is connected with the air exhaust end of the turbine booster air intake pipe and the air exhaust end of the auxiliary booster air intake pipe respectively through an air confluence valve; the low-pressure-ratio high-flow fluid machinery is arranged in the auxiliary booster air intake pipe; the air exhaust end of the intercooler is connected with the air intake end of an engine; the atmospheric pressure sensor is arranged at the air inlet; and the cooling fluid temperature sensor is arranged in a transmitter. Compared with the prior art, the diesel engine starting assistance system disclosed by the invention has the advantages that the start success rate of the engine at high altitude can be increased, and the start acceleration time of a low-compression-ratio diesel engine can be shortened, so that the diesel engine can enter a stable idling state more quickly.