The invention provides a calculating method for a power-cable magnetic-thermal coupling field. The method comprises the steps that 1, a power-cable electromagnetic field physical model and a power-cable temperature field physical model are built; 2, power-cable physical simulation models are built, and calculating parameters and boundary conditions are determined; 3, the corresponding calculating parameters are obtained by measuring a power cable; 4, an electromagnetic field and a temperature field of the power cable are solved according to the electromagnetic field physical simulation model and the temperature field physical simulation model; 5, if calculating results are convergent, the electromagnetic field and the temperature field of the power cable are obtained, magnetic-thermal coupling analysis is achieved, and if the calculating results are not convergent, iterative analysis is performed by returning to the step 4 until the calculating results are convergent. The calculating method is flexible in solving mode and very suitable for the magnetic-thermal coupling problems of processing cable loss and temperature rising.