The methods for estimating geothermal resources coexisted in oil and gas fields have been investigated and modified according to the difference between conventional and coproduced geothermal resources. The current status of geothermal resources coexisted in oil and gas fields in China has been reviewed and studied. The main factors that affect reservoir temperature have been investigated using numerical simulation. The modeling results showed that the decline rate of reservoir temperature decrease with the decrease in water reinjection rate but decrease with the increase in temperature of reinjected water. The advantages of power generation using geothermal energy coexisted in oil and gas reservoirs have been analyzed in comparison with using solar and wind energy. Some of the pilot projects of power generation using coproduced geothermal energy in the world have been appraised and discussed. "High efficiency method for producing oil-heat-electricity simultaneously" has been proposed after the feasibility of generating electricity using coproduced geothermal resources was proved. The method can meet the requirements from both enhanced oil recovery and developing geothermal energy. Finally, potential and prospect of efficiently developing and utilizing geothermal resources coexisted in oil and gas fields, especially electricity generation, have been analyzed and predicted.