The entropy production is expressed as the product of the generalized force (driving force) and generalized flux, which plays a central role in classical non-equilibrium thermodynamics. This expression has shortcomings in two aspects: first, the decomposition into generalized fluxes and forces is arbitrary to some extent; more importantly, the entropy production is negative value calculated in heat wave propagation, which breaks the second law. In this paper, we carry out analyses based on the thermomass theory and show that the entropy production is induced by the dissipation of thermomass energy during heat condution. The generalized force of entropy production is not driving force but resistive force, having a unit of force in Newton’s mechanics. The modified expression for entropy production not only guarantees its positiveness in propagation of heat waves consistent with the extended irreversible thermodynamics, but also avoids the arbitrariness of decomposition.