The rivers have many other functions，such as generating power，supplying water，preventing flood and protecting ecological areas，and how to balance multiple goals and achieve synergistic development and quantification of channel carrying capacity in channel construction has become one of the most important problems today. By using the modified variance coefficient，we carry out coordinated and adaptive regulation of channel carrying capacity combining with the horizontal evaluation value of channel carrying capacity on ecological，economic and multi-function utilization of river，calculate the maximum channel size under multi-objective coordination，take AE channel as an example to verify the rationality and operability of the evaluation model and calculation method. The results show that the maximum channel size calculated can alleviate the contradiction between current channel construction and economy，ecology and rivers，and multi-purpose utilization. The calculation model is reasonable and feasible.