Abstract: Isolated Streptomyces sp. S506 from tomato rhyzosphere is one of the beneficial strains which can promote root growth, control soil-borne diseases and attenuate root autotoxicity. In this paper, the effect of soil texture, temperature and moisture on Streptomyces sp.S506 colonization in tomato rhizosphere and growth-promotion effect of Streptomyces sp. S506 on tomato seedling were studied through pot experimentation. The results show that optimum soil texture order for Streptomyces sp. S506 colonization in tomato rhizosphere and the corresponding expression of growth-promotion function is loamy soil, followed by sandy soil and then clay soil. In the tested temperature gradient, the optimum temperature order for Streptomyces sp. S506 colonization is 30 ℃, 22.5 ℃ and the 15 ℃; and that for growth-promotion function expression is 22.5 ℃, 30 ℃ and 15 ℃ respectively. The optimum soil relative moisture order for colonization and growth-promotion function expression of Streptomyces sp. S506 is 20%, 25%, 15% and 30%. This study enhances our knowledge on the role of soil environment on the colonization and function expression of target strains in tomato rhizosphere.