The influence of load change by construction to water tube instrument at Shexian magnetic station was simulated by using point loading model,two-dimensional and three-dimensional loading models. The results showed that there was not obvious influence on annual and monthly variances of water tube instrument by loading change. The convergence values of two-dimensional and three-dimensional tend to be consistent. We found that the inner accuracies of water tube instrument decreased during the period of taking earth away based on the analysis of inner accuracies and operations of two components of water tube instrument.