Nowadays, a series of ecological problems caused by the greenhouse effect have had huge impacts on human beings' health, existence, manufacturing, environment and biological species. To avoid that, the emission of CO 2, the major greenhouse gas, should be reduced as soon as possible. Researchers have done a lot of work and suggested dozens of methods to deal with CO2. However, these methods do not fundamentally solve the problem of CO2. Recently, hydrothermal process is considered to be one of the most promising processes for the reduction of CO2, because the water of high temperature and pressure has remarkable properties as a reaction medium. In this research, the effect of Cu catalyst on the conversion of CO 2 into formic acid was investigated using Fe as reductant in water solvent. A series of experiments were conducted at different experimental parameters, e.g. amount of Fe (Cu), temperature, reaction time etc. Results showed that the highest yield of 46% for formic acid can be obtained under the following condition, Fe/Cu ratio of 1:1, CO2/Fe ratio of 1:6, filling rate of 35%, temperature of 300 °C, reaction time of 120 min.