This study outlines the effects of hypoxia stress on the behavior, physiology, immunity function, and key respiratory enzymes of Patinopecten yessoensis. To accomplish this, four dissolved oxygen (DO) gradients [1 mg/L, 2 mg/L, 4 mg/L, and 7 mg/L (control group)] were set to determine the behavioral characteristics (the degree of opening and closing of the shell), oxygen consumption rate, ammonia excretion rate, and the activity levels of antioxidant enzymes (SOD, CAT) and respiratory enzymes (LDH and PK). The results were as follows: (1) The survival rate of Patinopecten yessoensis decreased with the decrease in DO concentration; when DO was 1.0 mg/L, the survival rate was only 55%. At 1 mg/L, 2.0 mg/L, and 4.0 mg/L dissolved oxygen concentration, the median lethal time of the scallops was LT50=95.97 h, LT50=147.37 h, and LT50=209.58 h, respectively. (2) The behavioral characteristics of the scallops were divided into five grades numbered from 0 to 4; the higher the score, the better the scallop’s state. From the quantitative indicators of scallop behavioral characteristics, the lower the concentration of DO, the lower the score and the worse the state of the scallops. (3) Hypoxic stress had significant effects on the oxygen consumption rate and ammonia excretion rate of the scallops (P＜0.05) under the stress of DO≤2 mg/L. When the molar ratio of oxygen to nitrogen was ＜7, the energy supply of the scallops was mainly protein; whereas when the DO was ≥4 mg/L, the scallops were mainly sustained by protein and fat oxidation. (4) Hypoxia stress significantly affected the level of SOD, CAT, and respiratory enzymes (P＜0.05) in Yesso scallops. Being under 24-h hypoxia stress increased the concentration of reactive oxygen species (ROS) in the hepatopancreas and adductor muscle. After 48–96 h of hypoxia stress, the activity levels of the SOD and CAT enzyme began to decrease. The metabolic pathways are different under different concentrations of dissolved oxygen. The study has found that when DO=2 mg/L, the metabolism associated with aerobic respiration is converted to the glucose-pyruvate-lactic acid respiratory pathway and when DO=1 mg/L, the respiratory metabolic pathway may give priority to the glucose-succinate acid pathway. On physiological and biochemical levels, the decrease in immune function and the change in respiratory metabolic pathways may cause the changes in scallop behavior.