This paper proposes a kind of engineering riprap quantity calculation method based on ground penetrating radar(GPR) detection.The method is described in detail step by step.In the meantime,an example of riprap quantity calculation is quoted in Lianyungang city,China.At last,calculation methods and characteristics of engineering riprap quantity are summarized.The advantages and limitations of calculating method based on GPR to detect the ripped-rock are analyzed,and the method for determining the relative dielectric constant and the consideration are put forward.