Abstract: The highly or over matured source rocks were developed in the Sinian—Lower Palaeozoic sequence in the Sichuan Basin.By using iaser fluorescence induced microscope,many matrix types,such as marine vitrinite,marine inertinite,microme,bitumen and so on,can be identified.Using organic pe-trologic approach,the original matrix types can be resumed,which mainly are typeⅠand type Ⅱ.Based on the systematic determination of organic carbon in the source rocks,the original organic carbon can be restored with recovery coefficient of different organic types.The ordinary TOC of mudstone and shale was 0.21%～17.2%,The ordinary TOC of limestone or dolomite is 0.21%～17.2%.According to the maturity of marine vitrinite and bitumen,the R_o of the source rocks in highly/over matured stage is 2.36%～3.39%.The total hydrocarbon resources of the Sinian—Lower Palaeozoic is 2.14×10⁹ t,and the Leshan—Longnushi uplifted area is a favorable area for nature gas accumulation.