The behavior of dynamic desorption of He, H2, and CH4 from a cryosorption pump is experimentally investigated using a simplified technique to roughly purify unburned D-T fuel exhausted from a fusion reactor. As a fundamental study to dynamically separate the unburned fuel and impurities, the discharge rates of H2 (as a representative of D2 and T2), He, and CH4 (as major impurities) are determined as a function of time or temperature, when the cryosorption pump is regenerated from [approximately]10 K to the room temperature of 285 to 300 K according to the experimental date. It is found that H2 is adsorbed and desorbed on active charcoal independent of the adsorption sites of He and CH4, which are evacuated simultaneously. The present result leads to a simplified method for roughly separating unburned fuel from impurities in fusion reactors by controlling the desorption temperature.