The investigation of mineral resources below accomplished constructions is a new work proposed in recent years. At present, a mature and perfect method has not yet been formed. The authors analyze and discuss the controversial issues in the investigation of mineral resources below accomplished constructions, and proposes a method to determine the status of mineral resources below accomplished constructions: Use the orthographic images combined with construction land type patches to determine the scope of construction land; Use the width of the safety belt of the highest-level building, the maximum empirical value of the rock movement angle, and the maximum burial depth of the ore body to calculate the maximum covered width of the construction, and the estimated range of resource reserves is the remaining. By simplifying disputes and complex problems and optimizing the conclusions of the investigation, the purpose of carrying out the investigation reasonably and efficiently is achieved. This paper introduces the practical experience of Beijing, and puts forward some suggestions for further optimizing the investigation method. And the article can provide references for the implementation of the investigation method of mineral resources below accomplished constructions.