This paper describes the techniques of applying 5 m network high-precision gravity survey to engineering exploration, which include geodetic survey, gravity survey and three-dimensional inversion. Through the elimination of gravity influence on the engineering design parameters of the hilltop buildings, the human interference correction was realized. The forward calculation was made by using the precise forward formula for theoretical gravity anomaly of vertical prism, and the inversion was also conducted with the generalized inverse method. As a result, the structural characteristics of the top relief of the fresh granite batholith in the Shixiawei landslide-tackling area in Kowloon of Hong Kong were revealed. A comparison with the drilling result shows the reliability of the depth contour map for the top surface of the granite batholith.