The boulder distributed in granite weathering crust has great harm on the engineering construction. Accurately determine the size and distribution of boulder has important practical significance. In this paper, by adopting the combination of field measurement and numerical simulation method to study the performance characteristic of spherical boulder in the georadar detection. The following conclusions are drawn: There is an obvious of radar wave in the boulder reflection. The open width of reflex is increase with the boulder diameter and the buried depth. In radar wave,the radius of curvature of vertices has approximate linear relationship with the boulder diameter. And has Quadratic polynomial relationship with the buried depth. The conclusions obtained in this paper have a certain guiding role on analyzing georadar detection results about boulder.