Abstract: The compactness of foundation soil is one of the important factors affecting the m value of the horizontal resistance coefficient of the foundation. The compactness of foundation soil,with gravel soil as the foundation model material,is qualified by indoor physical simulation test. Through the horizontal static load test of single pile, the law of the characteristic value and m value of the horizontal bearing capacity of the foundation under different foundation compactness is obtained to provide a reference for the design of the pile foundation. The experimental study shows that: (1) Increasing compactness of the gravel soil foundation can significantly improve the horizontal bearing capacity and m value of the single pile; (2) The density keeps a linear relation with the m value of the foundation; (3) Density increase of the gravel soil foundation by 20% can lead to the amplification the m value by 1.39 times, and the horizontal bearing capacity characteristic value by 1.38~3.01 times.