The razor clam is wildly distributed in China, Japan, and Korea. The razor clam has high nutritive and economic value and is one of four marine bivalves produced in China. Artificial breeding and frequent inbreeding have decreased the genetic diversity of razor clams, and the germplasm resources are degraded. As a result, massive razor clam mortalities occur occasionally. Cultured clams are generally small and have poor disease resistance, and no superior commercial razor clam varieties have been bred for the commercial market. Therefore, improving genetic traits and breeding outstanding varieties of razor clams via artificial selection are primary goals of razor clam culture. In this study, six natural populations of (Zhejiang Xiangshang and Leqing populations, Fujian Xiapu and Changle populations, Jiangsu Sheyang and Shanghai Chongming populations) were selected as the F₀ material structure foundation populations, and continuous multiple-generational breeding (selection intensity:2.063) was carried out using the mass selection method. The growth difference between the F₅ breeding strain and a control population was compared. The selection response, realized heritability, and F₅ heredity acquisition were evaluated. The results showed no differences in egg diameter or fertilization rate between the F₅ generation (>0.05) and the control group. However, the metamorphosis rate, survival rate, and late growth in shell length of the F₅ generation were significantly superior to those of the control group (<0.05). Variations in the selection response of shell length, realized heritability, and heredity acquisition of F₅ during days 7-360 were 0.30-0.78, 0.14-0.37, and 4.83%-42.18%, respectively, and the means were (0.49±0.06), (0.23±0.08), and (26.49±11.73)%, respectively. These results suggest that continuous multiple-generational breeding of razor clams was effective, as it significantly improved survivability and the major economically important traits. Continuous selection of five generations of razor clams was effective, making further breeding to identify new razor clam varieties with desirable traits possible. The genetic gain in shell length was generally low, probably because of genetics and environmental factors. Razor clams are a mudflat bivalve that hide in silt, and their long body reduces adaptability to the environment. Hence, breeding should focus on weight selection to obtain more practical results.