Foam combination flooding is one of the most capable tertiary oil recovery techniques. For the pilot test of foam combination flooding performed in Sa-Nan, Daqing, gas hydrates affect the normal gas injection badly. The designed gas injection is 182 days, however, due to the influence of gas hydrates, only 59 days of gas injection is conducted. The injected gas is just about 36 days' work in the design. Based on the pilot test in Sa-Nan, this paper elucidates the structure, phase state and forming condition of gas hydrates and proposes a number of effective measures to prevent and remove the formation of gas hydrates in the process of foam combination flooding. Two models for predicting the forming condition of gas hydrates for foam combination flooding are presented in this paper. Phase-equilibrium-constant method is proved to be more accurate and reliable than empirical graphic method and is recommended for use in research work and field practice to determine the forming condition of gas hydrates in foam combination flooding. With this method, the forming condition of gas hydrates in Sa-Nan pilot is calculated. The result shows that gas hydrates will generate at temperature lower than 73.4°F. Three ways are proved effective to prevent the formation of gas hydrates for foam combination flooding, which are reducing the water content of natural gas, improving the injection technology to avoid the contact of water with gas and adding certain suitable inhibiting agent. Heating, lowering pressure and adding deicing agent are suggested as the three good measures to get rid of the plugging in injection pipelines caused by gas hydrates for foam combination flooding.