Abstract: Based on study of the component and its carbon isotope of natural gas samples from the Northeast and the East of Sichuan Basin,the genetic types of the natural gas in different regions are different.Natural gas in the Northeast was mainly derived from the over matured source rocks with type Ⅱ-Ⅲ₁ kerogen;besides,it is supposed that type Ⅱ-Ⅲ₁ organic matter makes more contribution than that of type Ⅰ₁-Ⅰ₂ type kerogen in this region.However,natural gas samples from Jiannan gas field(Upper Permian and Lower Triassic)showed that they were mainly generated by over matured source rocks with kerogen typesⅠ₁-Ⅰ₂ and part of gas showed characteristic of sapropelinite and humic organic matter origin.Furthermore,natural gas in Carboniferous pool was from the secondary cracking of oil derived from Silurian source rocks.