The kerogen separated from a sample of carbonate source rock was pyrolyzed under a constant high pressure (50MPa) for kinetic simulating experiment to probe into the genetic mechanism of gas generation from kerogen in marine carbonate source rocks according to the percentages of generating gaseous and non-gaseous hydrocarbons and the analysis of carbon isotope. By means of the Kinetics software, the kinetic parameters (activation energy and frequency factor) of generating methane (C1), ethane(C2) to pentane(C5) from kerogen are determined and the result is used in nature via extrapolation of laboratory kinetic data to very low heating rates in geological condition. It is indicated that methane (C1) is pyrolyzed from the source rock at Easy Ro=0.9,-2.9, (the conversion rate in the range of 10,-90,) and the other gaseous hydrocarbons (C2, C3, C4 and C5) generate at Easy Ro=1.1,-2.7, (the conversion rate being 10,-90,). This experimental result means that it can be a reliable model for effectively quantitative evaluation of marine carbonate source rocks.