SAGD twin well is an important technology for producing heavy crude oil, which demands a lot controlling about the two wells’ trajectory. It’s good to improve the drilling trajectory measuring accuracy and efficiency with the help of MGT technology instead of MWD. At present, there is no report on the application of similar mature instruments made in China. This article mainly introduces an experiment performed on the ground, which tries to find the relationship between the trajectory accuracy and magnetic source inside a casing to provide data and technical support to the practical application. A solenoid which is put into a 139.7mm casing as a magnetic emitter and a magnetic sensor are placed to simulate real drilling situations of SAGD, the relative positions of the twin well are finally worked out by computer analytic data. In the experiment, the relative position between the sensor and the casing is continuously changed to simulate the actual situation of bit drilling. 18 trajectory patterns are collected with 198 point sites data. Before correction, the average errors of calculated total distance was about 7% and the plane errors are about 9.4%; after correction, the errors are reduced to only half the previous ones. The results show that the calculated points can really reflect the actual direction of the trajectory.