For the purpose of studying effects of raw materials of a culture medium on its water content sand, sawdust and vermiculite were used at different ratios to blend into culture media. Water contents of the media were determined by the pressure membrane method. Stepwise regression analysis was done between the three raw materials and water contents of the media, and a regression equation was erected. Effects of the raw materials on water content were analyzed. The results showed that sand content had a significant inverse correlation with the water content; sawdust and vermiculite contents had a positive correlation with the water content. The three raw materials had a quite high positive direct effect on the water content of the medium, and each raw material had a positive indirect effect on the water content of the medium through the other two materials. Decisive coefficients were all higher than 0.80000, and the correlation coefficient R >0.890000; which shows that the regression model was effective, reliable, and fairly precise.