The invention relates to a method for constructing a head-expanded anchoring rod in sand-rich decomposed rock. The method achieves the aim that under the condition that engineering geology is complex, a steel sleeve wall retaining method, a common rock anchoring rod method and a jet grouting hole expanding method are used at the same time to achieve the aim of secondary cement paste hole cleaning. The method is the pertinence technological improvement for construction in the special geology of the sand-rich decomposed rock, and solves the problems of hole collapse, difficult anchorage, boulder facing and the like of the head-expanded anchoring rod in the sand-rich geology, the bearing capacity is greatly improved, the construction cost is saved, and the economical benefits are considerable. The method has the advantages of being innovative, practical and remarkable in effect, and enabling multiple practical and simple processing methods to be matched with each other to adapt to construction of the head-expanded anchoring rod in the special environment.