Abstract: Compactness of gravel core wall material is a key index for quality control of gravel core wall dam, which is usually detected by nuclear density meter. In view of the heterogeneous characteristics of the gravel soil, the compactness obtained by the mean value of maximum dry density in the conventional method is an approximate value. When the actual maximum dry density is greater than the mean value of maximum dry density, the calculated value of compactness is relatively large to cause misjudgment and affect the engineering quality. In this paper, the concept of compactness guarantee rate was put forward. Through two control indexes of compactness and compactness guarantee rate, the conventional method was optimized, and the evaluation process and criterion of optimization method were defined. Combined with the engineering example of Lianghekou Hydropower Station, it was proved that the conventional method is only a special manifestation of the optimization method. Finally, through the comparative analysis of the measured data in March 2019, it is found that the compactness degree tested by the conventional method is all qualified once, but there are some unqualified points when using the optimization method, which need further re-test. The optimization method is stricter than the conventional method, which improves the engineering safety margin and ensures the engineering quality.