The invention relates to a method for calculating the tracing contribution of a sudden accidental water pollution source at a point source, which is effective in rapid tracing of a river basin and environmental management and protection of the river basin. The method includes: according to the natural geographical features of the river basin, determining the control area corresponding to the control section of the river basin; using the monitoring data of the pollution source and the statistical data of the pollution source to budget regarding the pollution source in the river basin; using a one-dimensional unsteady water quality model to establish the relationship between pollution source and water quality of the section; using the relationship between pollution source and water quality of the section to calculate the contribution coefficient of the pollution source within the river basin and characterizing the contribution of pollution sources. The method is novel and unique, easy tooperate and use, accurate in calculation, and high in efficiency, makes full use of the basic information of the existing pollution source, quickly feeds back the state of the pollution source in theriver control section in a short time, locks the pollution source which has relatively greater contribution to the river water quality in the river basin, provides the support for the pollution tracing of the river basin, and is effectively used for the environmental protection and treatment of the river.