Plasma has a unique protective effect against high-power microwave attack. Based on the plasma fluid approximation method, the time dependent evolution of the incident electric field during the interaction between high-power microwaves and columnar plasma arrays was studied by using COMSOL software, and the physical process and mechanism of plasma protection against high-power microwaves were analyzed. The results show that the incident high-power microwave will change the plasma parameters drastically, especially the electron density will increase sharply, so that the plasma will show metal-like electromagnetic properties to the incident high-power microwave, and finally realize the effective protection against the incident high-power microwave. In addition, the plasma protection against high-power microwaves was experimentally verified by using columnar plasma arrays generated by high-frequency glow discharge. Finally, the main problems to be solved for plasma-based high-power microwave protection technology were summarized.