Abstract: By using orthogonal design, this paper systematically analysed the law of variation in chemical compositions of Chinese fir was from plantations, which with different ages and densities, and grown in different sites. The results showed that the degree to which each factor affects the chemical compositions of Chinese fir wood was determinated as: the frist is age, the second is site, and the third is density; Based on variation in chemical composition in the different ages, densities and sites, the better harvesting age of Chinese fir for pulpwood is about between 17 and 23 years.