Abstract: In order to develop a rapidly inversion algorithm for instantaneous release quantity on nuclear accident site, a calculation approach was established based on ensemble Kalman filter combined with Gaussian multipuff dispersion model. The influences of ensemble number, initial value and perturbation on inversion performance were discussed. The simulation experiment results discover that ensemble number of 50, bigger initial value and larger perturbation are relative optimal parameters. The time integrated release quantity relative error in simulation is less than 5%. The final results demonstrate a feasibility and validity of inversion algorithm based on ensemble Kalman filter, and this algorithm could sequentially track the variable source release quantity in real time in principle.