Abstract: The principle of declination surveying is introduced in this paper,the three main sources of error in the process of declination surveying are raised,they are:the Error of north magnetic direction measured by CTM-DI instrument、the Error of sign direction measured by CTMDI instrument、and the Error of azimuth angle measured by GPS between survey point and sign.The accuracy of each direction is analyzed using law of error propagation,and the calculation formula of mean squared error of declination surveying is inferred,on this basis,the accuracy of declination surveying in the current geomagnetic three-component observations is analyzed by living example.Integrating observation practice,several suggestions are given in improving precision of declination surveying.