The farming of the clam Meretrix lyrata has been successfully developed since 1987 and brought high economic and social benefits to the coastal communities. As a highly valued fishery resource especially in Vietnam, recently M. lyrata has become another new aquaculture species with a potential for large-scale farming in the South China Sea and a good market prospects. In this study, by adopting the ecology experimental methods, the effects of seawater temperatures, salinities, pH, and microalgae densities on the clearance rates of M. lyrata were investigated, which are expected to provide insight on culturing capacity, feeding behavior and energy of M. lyrata and references for healthy culturing and extension of M. lyrata.The results showed that the clearance rates of M. lyrata (P＜0.01) at three sizes were significantly affected by varied temperature (13～33℃), salinity (13～33), pH (7～9), and diet density(2.5×10⁴～10×10⁴ cell/ml). The maximum clearance rates of the large, medium, and small sized M. lyrata were 1.06, 1.78 and 2.42 L/g·h at 28℃respectively, 0.35, 0.65 and 1.05 L/g·h at salinity 23, 1.26, 1.67 and 2.02 L/g·h at pH 8,1.29, 2.07 and 2.29 L/g·h at microalgae density of 10×10⁴ cell/ml.These results indicate that the optimum feeding environmental conditions were: temperature 28℃, salinity 23, pH 8 and microalgae density 10×10⁴ cell/ml. These results indicate that the sensitivity of the large, medium and small sized M. lyrata to temperature, salinity, pH or microalgae density appeared in the following order: large size＜medium size＜small size.In addition, medium and small sized individuals had frequent feeding activity and stronggrowth vitality.