A novel flexible energy-use mechanism is proposed based on the energy coordination among electrolyzers, steam methane reforming (SMR) plants and gas-fired units in the day-ahead scheduling of the integrated gas-electrical system. The power-to-gas (P2G) energy conversion method provides an effective solution to the energy dilemma in China. Nevertheless, this method requires a high-value chain for application due to its high investment cost at present. Producing, and then selling, hydrogen via electrolyzers is more valuable than storing it for a later generation. The two hydrogen production methods of SMR and electrolysis can be combined with the operation optimization of electrical and natural gas systems to form a flexible energy-use mechanism. A model of the flexible energy-use mechanism is established. The model can be integrated into interdependent natural gas and electricity systems, aiming to alleviate the shortage of natural gas, improve energy efficiency and lower carbon emissions. To demonstrate the economic feasibility and carbon dioxide emissions reduction of the proposed mechanism, a bus-6 power system integrated with a node-6 natural gas system and an IEEE 30-bus system with a modified Belgian 20-node gas system are examined. It is concluded that the proposed flexible energy-use mechanism in the power and natural gas systems has higher economic value and lower carbon emissions than the power-to-hydrogen-to-methane-to-pipeline path.