According to recent studies that there are important differences in maximum light utiliazion efficiency（ε max ）among vegetation types

an estimation model of net primary productivity（NPP）

based on geographic information system（GIS）and remote sensing（RS）technology

is presented.This model has two significant characteristics;（1）NPP can be estimated just using ground meteorological data and remote sensing data.It is relatively easier to acquire data and its application can be enhanced.（2）After the validation with observed data and the comparison with other NPP models

the results showed that the predicted NPP was consistent with observed values

and it can more actually reflect the forest NPP than Chikugo model.In order to validate the NPP model

a case study in Inner Mongolia

China

was carried out.The results showed that the total annual NPP in Inner Mongolia in2002was390.8Mt C.The spatial changes of NPPwere remarkable

and it decreased from northeast toward southwest.Moreover

seasonal variations of NPP were also large.It was about72.7%of the total annual NPP in the three month of June

July and August

and the NPP values was very low（3.59Mt C per month）in January and February.