Abstract: The present invention provides a breeding method of a new variety of hard-shelled razor clams, comprising the following steps: a. Estimating the heritability of shell hardness trait: constructing full-sib families to estimate the heritability of the growth and shell hardness traits of the razor clams; b. Selecting individuals with hard shells from basic population using an electronic hardness tester of material mechanics as the broodstock clams; c. Artificially-induced spawning; d. The offspring grow-out; e. Purification of the new strain: with the new strain of hard-shelled generation 1 adults obtained in step d as broodstocks, repeating the steps c and d several times to obtain a new variety of razor clams with hard shells, and the shell hardness trait of razor clams has stable heritability.