The reaction properties of coke mixed with lump coke or powder coke in a CO2 environment could successfully lower the rate ofdissolving loss and enhance the quality of dry quenched coke. In order to investigate the dissolution loss mechanism of dryquenched coke mixed with different particle sizes, a homemade high-temperature coke reaction measurement device was used to study thedissolution loss reaction of carbon under various particle size ratios and different concentrations of CO2. The optical microscope analysis combined with the Coats-Redfern method were used to investigate the dissolution mechanism of dry-quenching coke with different particle sizes. The results indicate that the proportion of powder coke increases at various concentrations, that the powder coke dissolution lossrate is roughly 0.7-0.9 times that of the mixed coke, and that more CO2 reacts with the powder coke to produce a reactive carbon-solvation reaction, which increases the mixed coke dissolution loss rate of lump coke-powder coke as the proportion of powder coke increases.However, the isotropy of lump coke and powder coke decreases while the amount of anisotropic tissue increases significantly at different concentrations. In particular, the anisotropic tissue value of powder coke is on average 4% higher than that of lump coke, and itis more reactive. The activation energy of the reaction also decreases as the concentration of CO2 and the proportion of powder coke increase. The more powder coke there is in the coke at a given concentration, the more likely it is that the carbon-solvation reaction will occur. The amount of powder coke has a major impact on the rate at which mixed coke dissolves at low concentrations. The highest reductionin activation energy that occurs as the amount of powder coke increases is 30%. The research findings may offer a theoretical foundation forfurther reducing the dissolution loss rate of dry quenched coke.