Abstract: Quadrisyllable words and phrases with normal stress of mandarin were used to study the tonal coarticulation.It was found that the F_o perturbation at the start-point and the ending-point of the F_o curves in each syllable caused by tonal coarticulation larger than the difference of the intrinsic F_o of vowels at the start-point and the ending-point.As for the tonal coarticulation,it was further found that in general the coarticulatory effects are unidirectional,and the carryover effect does not extend to the endind-point of tone-section and the anticipatory effect does not extend to the start-point of that,and the F_o perturbation by tonal coarticulation has its pattern.It is highly probable that tonal coarticulation is conditioned by stress.Tonal coarticulation in word and phrase may be related to the speed with which word or phrase is pronounced.