Abstract: The automatic control of channel network is a key solution to the modern water-saving irrigation,and it is also a key technique problem of the Middle Routine of the South-to-North. Water Diversion Project.The design of controller demands a liner mathematical model,but the channel networks system is a high nonlinear system.A MIMO model of multi-channel system built in this paper is used to analyze the uncertainty introduced in the procedure of linearization;this uncertainty will be a precondition for the design of robust controller.If the liner model is taken as the standard one,the uncertainty is expressed by the largest singular value of the distance matrix of the models.And a simulation example of six-canal is given.