Taking the excavation of weathered granite by high-power cutter suction dredger as an example in Rizhao port，Shandong，we carry out the division of dredged region according to rock property，and establish the empirical formula based on the correlation between mechanical index standard penetration number of weathered granite and dredging parameters. Based on the relationship between productivity in dredging engineering，weathered granite distribution and mechanical property，we rank the dredging difficulty degree of weathered granite excavation on high-power cutter suction dredger，and it provides?a technical support for similar construction of dredging engineering.