The invention discloses a low-temperature starting system of a diesel engine. The system comprises a power source device and a combustion improver jet device. The combustion improver injection device is connected with a gas inlet pipe of the diesel engine. The power source device is connected with the power source input end of a starting motor of the diesel engine. The power source device comprises a super capacitor and a storage battery. The super capacitor and the storage battery are connected in parallel. The combustion improver jet device comprises a combustion improver tank, a liquid outlet of the combustion improver tank is provided with an electromagnetic valve, and the power source input end of the electromagnetic valve is connected with the power source output end of the starting motor. The combustion improver output end of the electromagnetic valve is connected with a combustion improver jet pipe. The other end of the combustion improver jet pipe is connected with a nozzle. The nozzle is connected with the gas inlet pipe of the diesel engine. The combustion improver jet device jets combustion improver to the diesel engine, the super capacitor of the power source device provides large cuttent for the starting process of the starting motor, the reliability of the starting process is ensured, starting time is shortened, and it is ensured that starting is efficiently and stably achieved within 5 seconds.