The invention discloses a method for determining a transformer winding time constant on the condition of different load coefficients. The method comprises the following steps of acquiring a transformer-related thermal coefficient, acquiring rated top-layer winding time constants (tauw, R) through fitting change between a hot point temperature and a top-layer oil temperature, and finally solving the winding time constant tauw through introducing relative winding time constants (tauw, pu). The method fills a gap in calculating the winding time constant on the condition of different loads and furthermore has advantages of simple calculation mode and easy acquisition of required information. Furthermore the method can lay a foundation for calculating dynamic change of the hot point temperature.