Abstract: In the diffusion of gas leaked from storage tank, the leakage intensity changes over time. However, the commonly used Gaussian diffusion model assumes that the leakage source is constant, which leads to a deviation between calculation result and actual situation. Instantaneous leakage releases air mass instantaneously, and continuous leakage can be regarded as a superposition of air mass in several instantaneous leakages. The leakage intensity of air mass in every instantaneous leakage is different. On this basis, the continuous leakage intensity and free air mass are discretized to improve the Gaussian continuous diffusion model. Therefore, a more theoretically-reasonable distribution function of ground gas concentration with time at different distances and intervals is obtained. This function is verified by ethyne tank leakage. The results show that the improved model can simulate gas leakage and diffusion with great leakage intensity variation and long leakage period at any time.