The rapid identification of source parameters (e.g., release locations, intensities, and number of sources) is of great importance for the numerical prediction of contaminant events, which helps to implement risk assessment and conduct crowd evacuation. In this study, an inverse method is established to estimate the source term of unknown releases. Validation of the proposed method is performed with a set of synthetic experiments. Results show that the algorithm is computationally efficient and can successfully reproduce the characteristics of multiple unknown point sources. To further assess the practicability of the method in the real world, uncertainty analysis is conducted with errors from measurements and wind fields. It is revealed that the method is relatively stable to uncertainties and can accurately estimate the number of sources and the grid cells where the sources are located. With the disturbed synthetic data, the relative errors of source intensities are all estimated within 15%. This study provides a perspective for source term estimation in the emergency response to a toxic gas leak or terrorist attack.