Abstract: It is generally outlined by the forerunners,that the down-concave longitudinal profile of the streams means that the greater the rate of increase of discharge downstreams, the faster the sediment concentration decreases, and the smaller the sediment constitution, the greater the concavity of the longitudinal profile is.In this paper,the features of the stream of longitudinal profile have been quantitatively described by means of the index of cencavity, the concave longitudinal profiles of the streams on the North China plain are not only the function of the river length, but also the function of hydraulic energy.At present, the adjustment of the channel gradient is only shown by the experimental formulas based on bed material and discharge, which can only reflect the action of exogenic force due to relative subsidence of the North China plain,and different movements inheriting from the original stucture, especially the features of the tilting neotectonic movement, the rate of crustal deformation, which is different in various geomorphic units, can influence the form of the longitudinal profile of the stream and the adjustment of channel gradient, which is the action of the endogene force.As the factors affecting the adjustment of the channel gradient are analysed, the affections of both endogene and exogenic forces must be considered, because the formation, the development evolution of fluvial landforms result in the comprehensive action of the endogene and exogenic forces.