Nonlinear chaos fractal study is a forward problem of nonlinear geomorphological theory, especially for fluvial geomorphology, and also is one of important boundary faces in intensive investigation on geomorphology. This kind of studies is just beginning at home and abroad. In this paper, based on the review of the studies on fractal in geomorphology, the fractal of different reaches and the river pattern on longitudinal profiles in the Lower Yellow R. and the Middle and Lower Changjiang River has been measured and tested. A preliminary study shows that, obviously, these is a fractal property in the longitudinal profile for alluvial river channels. Fractal value of channel longitudinal profile changes with time and space. A small vibration of fractal for longitudinal profile is able to cause difference and divergence in river pattern. It is related to envirenmental factors and hydraulic conditions, e.g. there exists a negative regression between fractal and gradient in the rever channel, which can be regarded as an evidence in analysing the evolution of river pattern and with which the development of longitudinal profile can be prospected.