The interaction of work and heat between Brownian particles in a bistable system, the external periodic force and the thermal stochastic force are analyzed. The stochastic energy balance equation based on Langevin equation is established. For the Langevin equation subjected to periodic force, stochastic force and damping force, the method of combining dynamics and non-equilibrium thermodynamics is used. From force as the foothold changed into energy as the research core, the exchange of energy between system and environment and the efficiency of doing work are deeply analyzed with this method when the Brownian particle motion is along single trajectories, which reveals that the bistable system exhibits stochastic energetic resonance phenomenon.