OBJECTIVE： To investigate synergistic effect of carbapenems combined with fosfomycin （FOS） on carbapenems-resistant Pseudomonas aeruginosa isolates from urinary tract infections in vitro. METHODS： The minimum inhibitory concentration  was detected using agar double dilution method. The fractional inhibitory concentration index was determined by checkerboard method. The effect of carbapenems combined with FOS on biofilm of P. aeruginosa isolates was determined using 96 crystal violet staining. RESULTS： 12 strains of carbapenem-resistant P. aeruginosa isolates were highly sensitive to FOS and amikacin， and were completely resistant to imipenem and meropenem. The combination of imipenem with FOS could induce a synergistic effect on 4 strains （33.3％）； meropenem combined with FOS could induce a synergistic effect on 5 strains （41.7％）； no antagonistic effect of carbapenems combined with FOS appeared. FOS combined with carbapenems could inhibit the biofilm of carbapenems-resistant P. aeruginosa （P＜0.05 or P＜0.01）. CONCLUSIONS： The combination of carbapenems with FOS possesses in vitro synergistic antibacterial effect on part of carbapenems-resistant P. aeruginosa isolates， the mechanism of which may be associated with inhibiting the biofilm.