Free hydrocarbon content(S

1

)is a frequently-used pyrolytic parameter in assessment of shale oil resource.However

light and heavy hydrocarbon losing during the process often yields result on the low side.For heavy hydrocarbon loss

we compared pyrolysed hydrocarbon content(S

2

)obtained through pyrolytic experiment before and after extraction of samples to estimate the lost heavy hydrocarbon of S

1

.For light hydrocarbon loss

we carried out Rock-Eval and PY-GC experiments on immature shale samples and gold tube experiment on crude samples to calculate the ratio of C

6-13

/C

13+

in different stages of maturity according to chemical dynamic theory and Easy R

o

model

then took this ratio as the ratio of residual C

6-13

/C

13+

in shale

and finally performed correction of light hydrocarbon lose based on S1 obtained after heavy hydrocarbon correction.Using the corrected parameter in assessment of shale oil resource made a great difference.Taking the E

2

s

4(2)

member in Damintun Sag

Bohai Bay Basin as an example

the result is only 22.6 billion tons without correction but 2.86 times higher (64.7 billion tons) after the corrected parameter was used.It is therefore suggested that correction of light and heavy hydrocarbon loss for residual hydrocarbon S

1

during assessment of shale oil resources is necessary.