An estimation method of regional grouting volume of karst cavern was proposed. It is difficult to evaluate the volume of karst cavern due to its wide distribution and various shapes. To solve this problem, this study used fractal theory to investigate the fractural property of karst cavern according to field data of geotechnical drilling, and the fractal parameters obtained were used to calculate the volume of karst cavern. The karst grouting coefficient, the ratio of grouting volume acquired in field to the calculated volume of karst cavern could be used to predict the total grouting volume of karst cavern along the tunnel with the calculated volume of karst cavern.