Abstract: Stress distribution situation at the joints weld and A and B type weld of a large air reservoir was measured and analyzed by adopting hydraulic pressure test. The data analysis results show that in the pressure range of 4.4-9.7 MPa, stress of all test points on the air reservoir increased linearly with the increase of test pressure, That was in the elastic strain range of material of the air reservoir. Stress at the joints weld of the air reservoir was the largest and stress at other positions was rather smaller. The large air reservoirs can run in security.