The invention discloses a biological effective dose determining method and system in tumor radiation therapy. The determining method comprises the following steps: establishing a cell survivorship curve description model by adding a correction parameter; acquiring cell survivorship data, and fitting the model parameters; establishing a biological effective dose model according to the cell survivorship curve description model; and determining a biological effective dose according to the biological effective dose model. By adopting the biological effective dose determining method and system in the tumor radiation therapy, the biological effective dose can be accurately determined, so that the change of different radiation therapy schemes can be more accurately performed; and in the obtainedcell survivorship curve description model, various parameters have corresponding biology significances, and the cell survivorship curve description model is simple and easy in clinical popularization.