We have previously presented a new coal flash pyrolysis method for drastically increasing the total volatile matter and the tar yield, in which the coal swollen by tetralin at 100-250-degrees-C was pyrolyzed in an atmospheric pressure of He. To examine the validity of the proposed method further and to examine the pyrolysis mechanism of the solvent-swollen coal, the flash pyrolysis of coal swollen by solvent was carried out for several coal-solvent combinations. Seven kinds of solvent were used to test the effect of the kind and the amount of radicals transferred. Ten coals of different rank were used to examine the radical acceptability of coal. Of the seven solvents tested, tetralin, a liquid derived from coal liquefaction, and phenol were very effective as far as the formation rate of the radicals from the solvent matches that of the coal fragment. The proposed method was more effective for the lower rank coals which have more oxygen functional groups. It was clarified that at least two mechanisms were involved in increasing the tar yield. The amount of radicals transferred by the two mechanisms, R(H,1) and R(H,2), were estimated from the yields of H-2 and H2O, respectively. The value of R(H,1) represented the degree of hydrogen transfer from the solvent to coal, which was controlled by the hydrogen donability of solvent and the hydrogen acceptability of coal. R(H,2) was related to the coal intramolecular radical transfer which is caused by the suppression of the cross-linking reaction of OH-associated hydrogen bonding.