Abstract: By experiment of long core samples from low permeability reservoir in Yanchang oilfield, the effects of cyclic injection volume,soak time, pressure decline rate, gas injection process and gas injection rate on low?permeability reservoir development by CO2huff?n?puff process were studied. The results show that the first cyclic CO2 huff?n?puff is the key of production, its soak time should keep stable pressure followed by opening well for production, after which the production can be conducted without keeping stable pressure at any cycle.And appropriate low gas?injection rate may well overcome the influence of the model heterogeneity, hence reducing the negative impact of gas fingering on reservoir exploitation