Abstract: Three rounds of exploration of marsel in Kazakhstan show that, the area has good petroleum geological conditions, but the exploration degree is low and the resource potential is unclear. The organic carbon content TOC is the standard of effective source rocks and is also the key parameters for the calculation of the amount of resources, however, the previous evaluation of effective source rocks and the calculated amount of resources are based on the residual TOC which gradually decreased with the mass hydrocarbon expulsion, so it will inevitably produce some errors. Therefore, to be more accurate, based on the TOC recovery coefficient formula, we recovered the residual TOC of source rocks, and then revised the criteria of effective source rocks, finally, calculated the resources of Carboniferous and Devonian in marsel. The results are as follows: for source rocks in marsel, the TOC recovery coefficient of carboniferous source rocks is about 1.6,while the Devonian is about 2.0; the revised lower limit of TOC for effective source rocks is 0.3% and 0.25% respectively for Carboniferous and Devonian; after TOC recovery, the total amount of recoverable resources is (2.62~5.10)1012m3 for the main source rocks in marsel. The effective source rocks evaluated based on the recovered TOC and the latter resources can reflect the quanlity of source rocks and the actual resource potential of marsel more accurately. It has a certain significance for the exploration of areas which are with low level of exploration, unclear understanding of resource potential as well as high degree of thermal evolution and low quantity of residual TOC.