Abstract: It is known that there are many examples of the thermal elimination of quaternary ammonium hydroxides which do not follow the Hofmann rule. Ye Xiulin et al. proposed the “conformation rule” for the elimination of quaternary ammonium hydroxides, and then, eight quaternary ammonium hydroxides were synthesised and subjected to the elimination. The results show that the conformational rule is superior and acceptable.DPCILO and CNDO/2 methods were used to calculate the conformational energy of some quaternary ammonium cations with different conformations andthe distribution of charge for studying the mechanism of Hofmann eliminaion reaction. The results show that the conformational rule, based on the conformational energy, can be used to explain the Hofmann elimination reaction well, but the elimination of straight chain alkyl groups other than the ethylic groups should follow cis-E_2 elimination mechanism instead of trans-E_2 one proposed by Ye Xiulin.