The strain G-Q7 producing PHB was irradiated respectively by UV, He-Ne laser and both of them to increase PHB production. The results indicated that the coordinative effect of UV and He-Ne laser was better than using them individually. The cells were treated firstly by He-Ne laser for 20 minutes and then by UV for 150 seconds, which resulted in a final cell concentration of 11.5 g/L, PHB content of 65%. The mutant had better hereditary stability. The two PHB polymers obtained from the strains G-Q7 and the mutant were analysed by the method of DSC and NMR, the conclusion appears that the mutagenic effect makes some certain enzyme of metabolism change.