The invention relates to a deformation-based real-time safety monitoring threshold determination method in an arch dam running period. The deformation-based real-time safety monitoring threshold determination method comprises the steps of building a mesh model for reflecting structure main characteristic; performing deformation value separation to obtain a water pressure deformation component; reflecting a dam structure material parameter; performing full-dam full-process simulation analysis, forecasting and developing dam deformation under conditions of a water level, a temperature, dam shoulder and creep within a certain time; performing water level, temperature, dam shoulder deformation and creep single factor deformation influence analysis by simulation analysis to obtain a deformationdevelopment rule; obtaining dam deformation under an actual condition by an interpolation algorithm according to the actual water level, the temperature, the dam shoulder deformation and the creep and by developing the water level, the temperature, the dam shoulder deformation and the creep; determining a deformation allowable fluctuation range according to monitoring and calculation deformation;and finally, obtaining the real-time deformation monitoring threshold. By the deformation-based real-time safety monitoring threshold determination method, the dam deformation is accurately forecasted, favorable explanation of a physical mechanism is achieved, meanwhile, the real-time dynamic change of an index is monitored, and real-time and accurate monitoring can be achieved.