The Manila clam, Ruditapes philippinarum, which is widely distributed along the coasts of China, is an economically important marine bivalve species in China's aquaculture industry. Global production of this species was 3.6 million metric tons in 2010. China is the largest producer of Manila clams, producing approximately 3.0 million metric tons annually, which accounts for about 90% of global production. In this study, the effects of clam size and sudden changes in environmental factors such as temperature, salinity, pH, and water flow rate on the burrowing speed of juvenile clams were studied under laboratory conditions. The burrowing rate of juvenile R. philippinarum was 100% at temperatures of 10-30℃, at salinity between 25 and 30, and at pH between 6.0 and 9.0. When salinity was suddenly changed from 30 to 10, 4-5 h into the experiment, burrowing ceased. When salinity was suddenly changed from 30 to 20, burrowing rate declined to 20-30% (T = 20℃,Zhuanghe clam) or 100% (T = 15℃, Fujian clam). There was no burrowing when pH was changed from 8.0 to 10.0. Using seawater (T = 15 or 20℃, salinity = 30, and pH = 8.0) as a control, burrowing time was prolonged when each variable was changed. Burrowing speed increased as the flow rate was increased from 3 to 4 and then 5 cm/s. The burrowing speed of 12 mm clams was the fastest among the three different shell sizes of juvenile R. philippinarum tested (6 mm, 9 mm, and 12 mm). Using ET₅₀ as an index, the optimum burrowing conditions were:T = 15-20℃, salinity = 25-30,pH = 7-9 (Putian clam) or 8.0 (Zhuanghe clam). Under these optimum conditions, some juvenile clams started burrowing after 1 min, 50% of the clams started burrowing after 3 min, and all clams began to burrow after 5 min. This study shows that abrupt changes in environmental factors had obvious effects on the burrowing behavior of Manila clams. Therefore, we suggest that it is important to pay attention to differences in environmental variables, such as temperature, salinity, and pH, between the place of purchase and the area where clams are to be reared. In addition, it is advisable to introduce clams to the farm when water flow is moderate and the shell length is more than 10 mm.