Abstract: Cementing in the long isolation section of large borehole in complex conditions can cause many problems,e.g.,gas channelling,lost circulation and blowout,difficulty of cement slurry returning to the designed depth and ineffective turbulent displacement,etc.A laboratory test on the performances of high density cement slurry was conducted,and this test was used to simulate the complex conditions of high-pressured salt bed and the coexistence of high-pressured and low-pressured formations in Well Kai-2 in Katemeric Structure of Qinghai Oilfield.The high density cement was used for cementing this well,and some associate technologies were also applied.The results were satisfactory,and some successful practices on cementing the long isolation section of large borehole in complex conditions,and gas channelling remedy work around the annular were applied.