Abstract: The gas generation behavior of residual bitumen in source rocks (in-source) by in-situ cracking and its effect on hydrocarbon generation from source rocks are examined through non-isothermal pyrolysis of whole rocks in a gold-tube simulation device. Results of the analysis using mudstone and sample extract from Kuangshanliang area show that residual bitumen in-source makes a significant contribution to oil and gas generation, and the yield of bitumen-cracked gas accounts for up to 32.3% of total gas yield from source rocks. The kinetics calculations indicate that the average activation energy for in-situ cracking of residual bitumen in-source is 234.1 kJ/mol, apparently lower than that for normal oil cracking in reservoirs. The maximum yield of hydrocarbon gases from Kuangshanliang mudstone is approximately 28.5 mg/g, substantially higher than that of the sample extract. Likewise, the activation energy for gas generation from Kuangshanliang mudstone is slightly higher than for the sample extract. Through a combination of experimental analysis, kinetics calculation and geological extrapolation, the threshold temperature for in-situ cracking of residual bitumen in-source is 140℃ only, approximately 30℃ lower than that for cracking the oil expelled (out-source). Additionally, results of whole rock pyrolysis with mudstone and sample extract from Maliuqiao area demonstrate that residual bitumen is the primary source of gas generation from source rocks of high maturity.