By using the drilling coring data

rock thin section

cast thin section

scanning electron microscope and logging data

and combined with the analysis of the test data

the diagenesis characteristics and its impact on reservoir porosity of Lenghu region of Paleogene has been carried on by the detailed study. The results showed that the maturity of the Lenghu region is low

the primary pore

secondary pore and micro cracks are both developed in the reservoir. The diagenesis types are complex

including compaction

cementation and dissol

ution. The compaction is the most fundamental reason for failure of reservoir. The porosity loss of the reservoirs in the study area caused of the compaction is 21.65 % in average. The cementation is an important factor for further reducing the reservoir pore loss

causing an average of 3.34 %. The dissolution of the reservoir is an important way to increase the hole

but due to the lack of dissolution fluid

its contribution is limited

increasing pores about 2.26 %. There is a positive correlation between the reservoir properties and maturity

and a negative correlation between the properties and depth

which show that the low maturity and deep buried Lulehe formation(E

1+2

)has the strongest compaction and cementation

and the worst reservoir property. The property of lower Ganchaigou formation（E

3

1

）was medium

and the upper of lower Ganchaigou formation（E

3

2

）

which has the highest maturity and is the most shallow buried has the optimal reservoir property.