This study investigated influences of the open/close states of pores and porosity distribution of activated coke on the mechanical strength of common activated coke for the purification of coal-fired flue gas by analyzing pore structure, abrasive resistance, and compression strengths of 9 types of desulfurization and denitration activated cokes. Research conclusions are conducive to disclosing the influences of porosity characteristics of activated coke for the purification of coal-fired flue gas on mechanical strength, decreasing the physical consumption of activated coke in the recycling of flue gas purification systems, and lowering the purification cost of coal-fired flue gas. According to research results, pores in the ranges of 0−2 nm and 2−500 nm of activated coke are further developed after recycling using the coal-fired flue gas purification system, and the average compression strength of activated coke is about 70% of the added fresh activated coke. However, the abrasive resistance of the recycled activated coke which has a smooth surface is higher than that of the fresh activated coke. Open pores are the main cause of reduced compression strength of activated coke. Open pores in the range of 2−500 nm can destroy the compression strength of activated coke the most. The open/close states of pores cause no significant impacts on the abrasive resistance of activated coke, but pores with diameters ranging from 0−2 nm can destroy the abrasive resistance of activated coke most significantly.