The invention discloses a method and system for adjusting error parameters in a power grid. The method includes the steps of calculating the percentage residual of state variables according to the residual values of the state variables of the power grid; comparing the percentage residual with the residual threshold value, if the percentage residual is larger than the residual threshold value, taking the state variables as question variables, and taking relevant branch circuits of the question variables as suspicious branch circuits; adjusting suspicious parameters of the suspicious branch circuits; judging whether the change of suspicious parameters can cause the change of the function value of a state estimation objective function of the state variables or not, and if yes, judging the suspicious parameters as the error parameters; modifying the error parameters, obtaining the modification values of the error parameters, and adjusting the suspicious parameters of the suspicious branch circuits into the modification values. Through the method and the system, data redundancy is not lowered, and meanwhile the accuracy of error data diagnosis is improved.