The effect of “zero time holding” quenching temperature on the 45 steel’s microstructure and mechanical properties were studied by the orthogonal regressive principle. The 45 steel’s microstructure characteristics with “zero time holding” quenched were analyzed. The results showed that the 45 steel’s strength and hardness increased with the increase of quenching temperature in the range of 780～ 900°C. The grain size in zero time holding was smaller than that with holding time (60 min). The martensite lath was very fine after “zero time holding” quenched. The mechanical properties of the 45 steel Processed by the zero time holding heat treatment is higher than those processed by the conventional heat treatment. The experimental results showed that the properties of the drive shaft with 45 steel were satisfying after they are processed with the “zero time holding”heat treatment technology.