GPS technology has been widely used in the plane control survey of tunnels and has exhibited great advantages. However, it is one of the topics worthy of study that how the results of GPS survey that is based on the normal line can be converted to be compatible with the traverse survey inside tunnels that is based on the plumb line, so as to minimize the influence of the plumb line deflection on the transverse breakthrough accuracy of tunnels. On basis of the basic theory of the plumb line deflection and the influence factors on the breakthrough survey of tunnels, the paper, taking works cases as example, presents the rule of the influence of the plumb line deflection on the transverse breakthrough survey and the corresponding countermeasures when GPS is used to establish the control net works of tunnels.