The invention discloses a method for judging the current operation mode feasibility of a power transmission line. The method comprises the following steps: building an environmental time-varying parameter discrete state space equation for an active power line loss of the power transmission line; estimating an environmental time-varying parameter by a kalman filtering method; with a present active power loss, a present current and the estimated environmental time-varying parameter of the power transmission line as initial known quantities, when a load of the power transmission line suddenly changes, giving a current operation mode of the power transmission line; estimating an active power loss track of the power transmission line through an active power loss difference equation according to initial values of known active power loss, carrying capacity and environmental time-varying parameter of the power transmission line, so as to obtain an active power loss sequence of the power transmission line, and comparing with the given maximum permissible active power loss of the power transmission line; if the active power loss is smaller than the given maximum permissible active power loss, judging the current operation mode of the power transmission line to be feasible; or else, judging the current operation mode of the power transmission line to be infeasible.