The authors employ the high-density resistivity method during an archaeological investigation of Sumicheng site，an ancient city of the Tang Dynasty，to find evidence of human activities and locate a favorable target for archaeological excavation in the southern part of the outer city． There are two obvious high-resistivity structures，the south wall of the inner city and an ancient building near the south gate along the outer city wall， of which the resistivities are indicative of rammed soil foundations． The south wall of the inner city is continuous but is cut off abruptly to the east，which we suggest it is due to either wall damage or destruction． The resistivity signature of the target area is verified by archaeological excavation，proving the feasibility and effectiveness of implementing the high-density resistivity method for archaeological exploration．