In order to explore the effect of RhlA and RhlB gene expression on viscosity reduction in microbial oil recovery，a real-time fluorescent absolute quantitative（Q-PCR）method for RhlA and RhlB genes was established，and the Pseudomonas aeruginosa X7 fermentation broth and Karamay Oilfield at different culture stages were detected. The expression levels of RhlA and RhlB genes in different formation waters were measured，and their rhamnolipid production，surface activity，emulsifying activity， emulsifying stability，and crude oil viscosity reduction rate were determined. The results showed that the expression levels of RhlA and RhlB genes were positively correlated with rhamnolipid production，surface activity，emulsifying activity and crude oil viscosity reduction rate. With the increase of fermentation time，the expression levels of RhlA and RhlB genes in the fermentation broth increased continuously and reached the maximum at 24 h，then decreased and stabilized at 60 h，and the maximum expression levels of RhlA and RhlB genes were 2.51 × 10⁶ and 3.25 × 10⁵ copies/μL. The highest expression level of RhlA and RhlB genes reached the maximum value of 824.08 mg/L at 60 hours. The surface activity of the fermentation broth，crude oil emulsifying activity and heavy oil viscosity reduction rate also increased with the increase of fermentation time and reached the maximum value at 24 hours，48 hours and 60 hours，respectively. The rhamnolipid crude extract in the fermentation broth had good stability and could work stably under certain extreme conditions. RhlA and RhlB genes probably affected microbial oil recovery by affecting rhamnolipid production，surface activity，emulsifying activity and viscosity reduction rate of crude oil. This study preliminarily revealed the influence of functional gene expression related to biological surface activity on the viscosity reduction effect of heavy oil，which was important to promote the industrial application of microbial oil recovery.