A modular thermo-activated wall (MTAW) with special internal cavities for filling thermal diffusivity fillers is proposed to solve the problem of low-grade heat accumulation which restricts the improvement of heat injection efficiency of thermo-activated walls. The dynamic heat transfer model of MTAW was established., and performance differences between MTAW and two reference walls were compared based on typical winter conditions of the cold climate zone. The effects of the inclination angle (θ) and geometry size of the filler cavity (a:b), and thermal conductivity of the filling material (λf) on energy-saving potential and economics were discussed. Results show that the application of the filler cavity inside the wall and the filling of thermal diffusing material have a significant saving effect on the total operation energy consumption and operation cost. Compared with the two reference walls, when the long axis of the MTAW filler cavity is transverse and a:b is 1:2, the total operating energy consumption can be reduced by 2.60% and 14.13%. Compared with the two reference walls, the total operating cost of MTAW can be reduced separately by 12.41% and 50.04% respectively. When the long axis of the filler cavity is inclined to the room side, the heating energy consumption decreases first and then increases with the increase of θ, and the performance indexes are better when θL is 60°. The a:b and λf are inversely proportional to the total operating energy consumption and operating costs, and the reduction rate of heating energy consumption and operating gas cost can reach 3.03% and 34.53% respectively when the λf is 12λc.