The invention adopts the technique of combining traditional breeding and molecular breeding. Firstly, a key gene of genK is knocked out, the metabolic flow of gentamicin C1 is blocked, a micromonospora purpurea engineering strain Gb1088 is obtained, and components, C1, C2, C2a and G418, of the metabolic pathway of gentamicin C1 are no longer synthesized; then a genL-knocked micromonospora purpureaengineering strain Gb1098 is built. The strain does not synthesize gentamicin C2b, nor synthesizes the components, C1, C2, C2a and G418, of the metabolic pathway of gentamicin C1, and specificity synthesize gentamicin C1a. The new species micromonospora purpurea engineering strain Gb1098 has a fermentation unit of 1098 units/mL, the components are monotonous, extraction and refining are convenient, chromatography separation is not adopted, industrial production of gentamicin C1a is greatly facilitated, the key technical problems which have not been solved internationally in industrializationare solved, and the requirements of industrialization are met.