Abstract: Enzyme engineering is one of the subject in biological technology, has a widely effect in agricultural products processing. Natural enzymes often cannot fit the actual production, so the enzyme modification and mutant library screening are necessary. At present, there are two main ways for enzyme evolution, including point mutation and directed mutation. Establishment methods of mutant libraries are mature relatively, and the capacity of libraries can meet the requirements. But the screening methods of mutant libraries are restricted by existing techniques, and become the bottleneck of the directed evolution technique. This paper introduces several common methods for mutant library screening, elaborates the principle and characteristics of these methods, and the future development direction and trend are summarized.