Abstract: The theoretical basis of traditional power system state estimation is the law of large numbers based on traditional statistics,that is,when the number of measurements approaches infinity,the estimated value approximates to the true value with 1 probability.However,the number of measurements in the actual system is limited and sometimes even small,there is no theoretic guarantee for the evaluation index and estimation precision of the traditional state estimation.In view of this situation,the paper introduces the concept of uncertain measure under the uncertainty theory system,and explains the difference and relation among the uncertain measure,uncertainty of measurement and measurement error in the state estimation.Furthermore,the normal measurement,abnormal measurement and normal rate are redefined under the uncertainty theory system.And a new evaluation index of state estimation result considering the normal rate and the measurement deviation degree from the true value is proposed and the rationality is proved.