Abstract: The changes of total dissolved CO2 in surface water in tropical Pacific (10°S-20°N, 120°E-90°W) during El Niño and La Nina events have been numerically simulated using a three-dimensional global ocean carbon cycle model with biot a pump. The simulated results show that the changes of total dissolved CO2(TCO2) and partial pressure difference between sea and air(PCO2) in northwest Pacific(0-20°N, 120-150°E) and in central and east equatorical Pacific(10°S-10°N, 150°E-90°W) were not iceable. During El Niño events, TCO2 and PCO2 were increased in northwest Pacific and decreased in central and east Pacific; There were opposite changes in both regions during La Nina events. The simulated change trends of TCO2 and PCO2 are consistent with observations.