Steroid compounds plays an important role in physiological and pharmaceutical effects and the market demand is very huge. The microbial transformation process of steroid compounds and their key steroids is gradually applied since its application offers a number of advantages over chemical synthesis as follows: regio-stereoselectivity, reducing the synthesis procedures, shortening the production cycle, improving yield, more eco-friendly process and so on. However, the mechanism of microbial catabolism of steroids is still to be further explored and determined. The essay comprehensively analyzes the structure types and main sources, physiological functions, microbial transformation and catabolic mechanisms of steroid compounds and focuses on the key enzymes and their molecular mechanisms of metabolic process of steroids, which can provide a reference for construction of engineering strains and the development of industrial production technology for microbial transformation of steroids.