Some unfavorable geological conditions can affect the construction of tunnels． In order to evaluate the damage degree of tunnel construction and determine the surrounding rock grade and stability of the tunnel，the authors used high-density resistivity method to detect the surrounding rocks of Shimodong tunnel in Xicheng Town of Helong City． The underground resistivity structures of the entrance，exit and middle parts of the tunnel are obtained． Through analysis，it is found that there are no bedrock faults near the tunnel，although some joints and fissures are developed in some locations，which are characterized by low-resistivity anomalies． The tunnel structures are stable overall，favorable for safe and efficient construction． The study also proves the good application effect of the high-density resistivity method in tunnel safety detection.