To investigate the deterioration process of concrete in severe cold areas under coupled freeze-thaw and leaching action, an experimental study was conducted using an alternating method of rapid freeze-thaw cycles and immersion in ammonium chloride solution. This study examined the time-dependent evolution laws of the physical and mechanical properties and microstructure of concrete, quantified the coupling effects of freeze-thaw and leaching action, and established a predictive model for the degradation of mechanical properties. The results show that under the coupled freeze-thaw and leaching action, both the leaching depth and the amount of calcium leaching increase linearly with the equivalent service duration, while the compressive strength and splitting tensile strength exhibit a negative exponential decay trend. A significant synergistic effect was observed when freeze-thaw and leaching acted concurrently, with the acceleration factors for strength degradation and mass loss rate reaching 1.2 to 1.5 and 20, respectively. The reasons are that freeze-thaw action leads to an increase in porosity and increases the number and width of micro-cracks, and the leaching of solid-phase calcium promotes smoother and larger pores. Furthermore, the temporal evolution of compressive strength damage under individual freeze-thaw, individual leaching, and coupled conditions consistently follows an inverse S-shaped curve pattern.