Abstract: Circulation loss has occurred many times during drilling Well PATOLON-2. During the plugging treatment, if high pressure layer is penetrated, gas kick ofen occures. If the mud density is higher than 1.30 g/cm3, circulation loss happens in upper well section, and if the mud density is lower than 1.42 g/cm3, gas kick happens in bottom well section, which is a very complex wellbore condition. To conduct geology logging and cementing the ￠339.7mm technical casing, the mud density for the upper section, 0-1 345 m, was selected as 1.30 g/cm3, and 2.0 g/cm3 was selected for the lower section, 1 345 m to bottem. Drillpipe injection and annlar injection were taken to inject cement and it satisfied with the need of clean wellbore, stable pressure, no leakage, no gas crossflow during cementing. The high pressure gas well cementing operation was completed with high quality, combined with pilot slurry, weighted spacer, slurry with the characters of microswelling, and loss and gas crossflow preventing, and double plugs. The success of the well cementing work supplies a reference for similar complex well cementing.