Abstract: The parallel heading is normally used as the transportation channel during construction and the evacua? tion or drainage passages during operation for long mountain tunnels in complex geological conditions, especially in rich groundwater condition . But there is little thorough study of the influence of parallel headings on groundwater distribution around the main tunnel. On the basis of existing parallel heading design, and considering several affecting factors, such as height of water head, grade of surrounding rock, horizontal spacing and vertical height difference between the main tunnel and the parallel heading, the effect of the parallel heading on the water pressure around the main tunnel was calculated and analyzed. The results show that the decreasing amplitude of water pressure is large for the tunnel with high initial waterhead after installing the parallel heading; under different grades of surrounding rock, the decreasing amplitude of the waterhead of the main tunnel increases with the decrease of permeability coeffi? cient of rock mass, the better the surrounding rock is, the better effect the drainage of the parallel heading is; the horizontal clearance between the parallel heading and the main tunnel should be determined by giving priority to consideration of construction organization and safety, and generally 20 m is recommended; vertical position changes have little effect on water pressure distribution and it′s unnecessary to have a large vertical height difference.