Abstract: 【Objective】 To select vermiculite from southern Xinjiang compounded with mushroom slag and furnace slag, and to screen the substrate formulation suitable for seedling of pepper in South Xinjiang greenhouse. 【Methods】 The experiment was conducted in the greenhouse of Tarim University Horticultural Experiment Station from May to July 2021.The experiment was conducted in a randomized group design with pure vermiculite as the control, and seven treatment groups were set up to determine the physicochemical properties of different substrate formulations and the growth and physiological indexes of pepper such as plant height, stem thickness, root area and soluble sugar content. 【Results】 CK (pure vermiculite) could provide a good root growth environment for pepper, and the physicochemical properties of all treatment combinations met the standards of pepper seedling substrate except for T₂ (vermiculite∶ slag∶ mushroom slag volume ratio of 1∶0∶1) and T₄ (vermiculite∶ slag∶ mushroom slag volume ratio of 1∶1∶1) treatments.The maximum height of T2 plant was 8.5 cm, the thickest stem thickness of CK was 1.59 cm, the maximum leaf area of T₇ (vermiculite∶ slag∶ mushroom slag volume ratio of 4∶1∶1) was 4.41 cm², the maximum seedling emergence rate of CK was 90%, and the best root growth was 93.25 mm for the main root length, 511.29 mm² for the root area, 21.33 root tips, and 49.8 mm for the average root length, respectively.49.8 mm, and the physiological indexes of T₁ (vermiculite∶ slag∶ mushroom slag volume ratio of 1∶1∶0) were relatively optimal as 0.62 mg/cm² for Chl a, 0.82 mg/cm² for Chl a+b, 0.53 mg/cm² for Caros, 0.66 mS/cm for soluble sugar, 0.78 mS/cm for soluble protein.The highest Chl b and Anths content of CK was 0.25 mg/cm² and 0.04 mg/cm² respectively. 【Conclusion】 After the comprehensive evaluation,the conclusion is obtained, that is, the synergistic properties of mushroom residue and vermiculite are poor and unsuitable for mixed use in the cultivation of pepper seedlings; the synergistic properties of vermiculite and slag are better, and the analysis of principal components and comprehensive evaluation shows that under the greenhouse conditions in southern Xinjiang, CK (pure vermiculite)is suitable for cultivation of pepper seedlings.