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.