In China

the spherical intrusive bodies are wide distributed and have obvious influences on the evolution processes of organic matters in some sedimentary basins.Adopting such a physical model as the"cooling of spherical body in infinite solid medium"

and taking the Fourier's heat-conduct law as a basic hypothesis

the heat-conduct equation for heat-releasing process after magma crystallization and its solution have been obtained by the author. On this basis

the temperature distribution equation of coexistent bodies of magma and igneous rock have also been discussed.If the symbol α

c

shows the residual ratio of available kerogen at any point P in surrounding sedimentary rocks

α

0

is that of kerogen which is far from intrusive body and have

not been influenced by magmatic heat

then the ratio η=α

c

/α

0

=exp[-K

0

(θ—t

c

)

]

may indicate the extent of influence of magmatic heat on the evolution of kerogen. Here

K

0

is the facter of reaction rate depended on Arrhenius formula

and θ—t

c

=θ—θ

0

is the magmatism index (MI).The geochemical data collected show that the method for evaluating the influence on kerogen proposed in this study is helpful to quantitative prediction of thermal evolution of organic matters.