Regarding the state's policy that gtves a higher on-grid electricity price to natural gas CHP (combined heat and power) projects,this paper studies the effect of it on the operation of those projects by theoretical analysis and a case study,It concludes thar on-grid electricity price on the high side,compared to heat price,will lead power plants to produce more electricity but less heat,thus catusing decrease of the plants ' thermal efficiency and harm to energy saving of the whole society.