Acute toxicity of low pH to Marsupenaeus japonicus was studied by hydrostatic experiment. We selected Marsupenaeus japonicus with an average length of (48.87±4.81) mm as experimental subjects, and set pH gradient as Marsupenaeus japonicus3.8, 4.1, 4.4, 4.7, 5.0 and pH of control group as 8.0±0.1 to investigate the mortality of Marsupenaeus japonicus under low pH stress and analyze the semi-lethal concentration (LC50) and semi-lethal time (LT50) of Marsupenaeus japonicus under pH stress. The results showed that: the mortality of Marsupenaeus japonicus increased with time under the same pH. There was a negative correlation between the mortality of Marsupenaeus japonicus and the pH in water (R<0, P<0.01) at the same stress time. The LC50 of Marsupenaeus japonicus under stress of 48 h, 72 h, 96 h with pH was 7.907×10-5, 5.14×10-5 and 3.673×10-5 mol/L, and safe concentration (SC) was 3.673×10-6 mol/L, corresponding pH was 4.102, 4.289, 4.435 and 5.435 respectively. The LT50 of Marsupenaeus japonicus under water pH=4.1, 4.4, 4.7 was 58.821, 93.771, 139.549 h respectively. This study provided a basis for studying the breeding of Marsupenaeus japonicus, the tolerance to low pH and the selection of low pH resistant strains.