Abstract: A substation three-phase nonlinear state estimation method based on zero impedance branches is presented in order to eliminate topology and analogy errors at substation level and accordingly enhance the control center state estimation reliability and accuracy.Measurements from different apparatus are utilized in substation,such as remote terminal unit（RTU） and phasor measurement unit（PMU） three-phase data.A breaker-oriented nonlinear three-phase state estimation model is established on Kirchoff’s current law（KCL）,in which analog bad data and topology bad error identification can be decoupled,realizing real-time three-phase unbalanced degree monitoring at substation level.It is shown that this method is very fast and easy for implementation and can provide high measurement redundancy and reliable results.The test results show that the proposed approach is very effective.