In this paper，the recombination rate of charges in low density polyethylene （LDPE） film was obtained by measuring the number of photons released from the film when the film was short-circuit discharged after being set to high voltage of direct current （HVDC）. Under different designed conditions, including changing the polarity of HVDC and the value of applied field and the time duration of applied field，the amount of photons was measured to calculate the charges’ combination rate. The result showed that the measured number of photons （recombination rate） was sensitive to the applied field but insensitive to the applying duration. When the field was higher than 80 MV/m，the number of released photon increased slowly with increasing voltage. Using the date obtained in our experiment as well as those in other papers，the luminous efficiency of LDPE film was calculated to be 5.9×10-6，and the charges’ recombination rate during first 0.2 second at the beginning stage of short-circuit is around 2.8%.