Abstract: Reservoirs in the Chang-8 Reservoir in the Honghe Oilfield are characterized by tight formations and well-developed natural fractures that give rise to water channeling during water injection. Under such circumstances study and field tests have been conducted to ameliorate the situation by using gelation technologies in horizontal water injectors with severe water channeling. Taking viscosities of plugging gel as evaluation criteria, the formula of polymer gel water-plugging agents was optimized and their aging, salt-resistance, shear resistance, plugging and anti-flushing performances were evaluated under simulated conditions of the formation. Test results showed that polymer gel water-plugging agents have adjustable gelation time of 4-10 days with salt resistance of 1×105 mg/L, Ca2+ mass concentration of 8 000 mg/L, high shearing and flushing resistance and resulting plugging efficiencies over 95%. Field tests were performed in 2 wells and they demonstrated that productivities were enhanced and the watercut reduced in the oil producers. In 217 days, incremental oil production was 102 t, while the watercut fell from 99.0% to 92.3% and effectively maintained that rate. Study and test results showed that the application of gelation technologies in horizontal wells can effectively plug prevailing water channels, and remove water channeling among horizontal water injectors in Honghe Oilfield.