The invention relates to the technical field of oilfield development and maintenance, in particular to a method for rapidly determining water-injection starting pressure of wellheads in all small layers of a water injection well. The method utilizes interpretation results of two tests on a water injection profile of each small layer of the water injection well to obtain two different water injection flow of each small layer, and connect two coordinates of each small layer including an X-coordinate representing daily water absorption amount and an ordinate representing water injection pressure value of each wellhead to form a straight line acting as a water injection indication curve of each small layer. The water injection starting pressure of a wellhead in each layer is an intercept formed after the water injection indication curve extends and intersects each ordinate at a point. The method only utilizes two interpretation results of two tests on a water injection profile of each small layer to process data, draw dots and lines so that starting pressure of each wellhead in each small layer. High in adaptability, easy in operation and few in investment, the method is capable of accurately measuring wellhead-starting pressure of thin interbeds and of all small layers at different depth.