Railway tunnels are always located in mountains. As a result of uneven topography, dense vegetations and complex terrain, it is difficult to carry out the survey works. For long tunnels, GPS survey is the favorite method. Due to the limit of the topography and terrain conditions, however, the selection of the GPS control points and the arrangement of the control network can not meet the requirements of the corresponding specifications. Based on the application of GPS control survey in Huanggou tunnel on DalianMudanjiang railway in Northeast China, the author presents the complete GPS survey process for long tunnels in complex geographical conditions, including GPS control network establishment, survey scheme determination, survey execution, survey data processing, survey result verification and analysis and survey result application. The above technologies guarantee the highaccuracy breakthrough of the tunnel. The paper can provide reference for similar projects in the future.