Water pollution accidents occur frequently, and timely acquisition of relevant parameters of pollution source is needed to carry out emergency treatment. This paper presents a new method of two-dimensional instantaneous point source parameters inversion based on least square method. Firstly, the analytical solution of two-dimensional instantaneous point source is used to generate the observed data of hypothetical examples. Then the proposed method is used to process the observed data, and the parameters such as pollutant emission position and time, emission intensity and longitudinal dispersion coefficient are obtained. This paper explores the influence of observation data errors on the inversion results, as well as the influence of the number of monitoring points. The results show that the method can get the source parameters and key hydrodynamic parameters of two-dimensional instantaneous point source simultaneously. The inversion results are less affected by the errors of the observed data; the number of observation data also has an effect on the inversion results, but the effect is not significant; this method can be used in practice.