The invention belongs to the field of biomass energy utilization, and discloses a preparation method of biomass-based porous carbon and a product. The method comprises the following steps: S1, mixingbiomass particles and an organic potassium salt or an organic sodium salt, heating and drying a mixture to obtain a porous carbon precursor; S2, heating, pyrolyzing and carbonizing the porous carbon precursor in an inert atmosphere, and then performing heat preservation; S3, performing acid pickling on the mixture, removing an alkali metal salt, then filtering and flushing the mixture with an excessive amount of deionized water till the filtrate is neutral, and performing drying to obtain the biomass-based porous carbon. The invention further discloses a corresponding product. According to thepreparation method, the preparation conditions are adjusted, the biomass is subjected to catalytic carbonization by adopting an activating agent, and the activating agent catalyzes the carbonizationand coking of the biomass, and is fully in contact with coke particles for further activation to generate micropores in order to obtain the biomass-based porous carbon with a large specific surface area. The method is simple, is a green and sustainable preparation method, and has wide applicablity for different saccharides and lignocellulose biomass raw materials.