A new tortoise coordinate transformation is defined. With the thin film model , we calculate again the temperature and the entropy of non_stationary black holes. The problem of indetermination of the cut_off factor in calculating the entr opy of non_stationary black holes is solved. We study and understand again the t emperature and the entropy of non_stationary black holes by way of the Vaidya b lack hole and the rectilinearly accelerating black hole.