Abstract: This paper presents the evaluation of the engineering geological conditions for a large tunnel crossing Yellow River at Zhongwei.The tunnel is to transport gas from the western China to-the eastern China and is 1197.7 7m long and 4.3 m high and 5.6 m wide.The elevation of the tunnel ceiling is 1130 m above the sea level and 100 m below the Yellow River.The surrounding rocks are the Cambrian rocks,Mopanjing Formation and include celadon and silver-gray metamorphic medium heavy bedded fine-granular feldspar quartz sandstone and phyllitic slate and sericite phyllite.The class of the surrounding rock quality is III-IV.The permeable ratio is between 4 and 67 Lu,the P-wave velocity is from 500 to 3300 ms-11.The BQ value is between 300 and 400.Modulus of deformation is between 6.11 and 9.22 GPa.Poissons ratio is between 0.14 and 0.24.The internal friction angle（） is between 42.1 and 44.7.The groundwater is the water in fissures of the bedrock.The aquifer supplied by atmospheric precipitated water is the agnostogenic rocks of the Cambrian system.The seepage capacity of a signle well is 1.0 ～50 m3 per day.The traverse rock tunnel axis is from relative intact to relative broken rocks,and has no active faults.The alignment and depth of the tunnel design is adequate and feasible.The construction and long-term operation are safe.