In order to study the relationship between the salt expansion amount and moisture content ,salt content ,dry density ,the overlying load, we design the sulfate saline soil salt expansion test quantitative humidifying independently and make use of the BP neural network to forecast the amount of salt expansion on the basis of the experimental results .We found that the prediction value that the adaption of BP neural network to different moisture content, salt content, dry density and overlying load level condition is near to the actual value. We prove that it is feasible to use the BP neural network to predict the amount of salt expansion, which offers a new idea to predict salt expansion.