Abstract: In order to study the acid generation of Acacia wood during autohydrolysis and its influence on the chemical properties of sulfate pulping of hydrolyzed wood chips, the wood chips autohydrolysis was pretreated in the P severity range of 93-1 008. Then, a part of the pretreated wood chips were washed by ultrasonic wave to remove the residual acid. The pre-impregnated wood chips treated with acid removal and the control sample(i.e. without ultrasonic treatment) were sulfate pulped under the same conditions. The results showed that the content of acid in autohydrolysate(AHL) increased with the increase of pretreatment intensity, resulting in the pH value of AHL decreased. Among them, acetic acid was the main acid component. The concentration of acetic acid reached 4.21 g/L at P factor of 606, which slowly increased to 4.41 g/L at 1 008, and a small amount of formic acid was also detected. The results showed that the pulp yield of wood chips increased by 10.1% after ultrasonic washing, and the Kappa value of pulp decreased from 31.2 to 19.7 when the P factor was 1 008. The pulp viscosity did not change significantly, while the fiber length decreased from 0.76 mm to 0.64 mm at the P factor of 1 008, which may be the reason of the slight decrease in the tensile and breaking strength of wood chips after ultrasonic washing.