A "convenient calculation" of MTTp = 0.1 FVC/2 Vp was derived from the principle of Jordanoglou to measure the partial mean transit time (MTTp). It was used to calculate the MTTp from the maximal expiratory flow volume (MEFV) curve of 342 healthy young children. The multiple regression equations were built with age, height and FVC as independent variables. The result showed that the MTTp of all children were elongated with the decay of lung volume with a similar rule as in the old, middle-aged and young people. No regular changes of MTTp in age groups were noticed. The regression equations showed that the MTTp of boys were positively correlated with FVC; while those of girls were negatively correlated with age; besides, MTT20-30% and MTT70-80% were positively correlated with FVC. The age and FVC just had the opposite effects so that little regular changes of MTTp occurred in the age groups.