This paper presented a new approach to realize the optimal distribution of auto-control valves in water supply network by hydraulic calculation. Firstly, the local headloss of the auto-control valve was introduced to the pipe network's hydraulic calculation. Then, the valve was supposed to be set on each pipe with different opening degree, following which the influencing degree on network was calculated under each situation. Last, this approach was tried on an example water supply network, and a general principle for the optimal distribution of auto-control valve was obtained. Through application it could be found that this approach was practical, easy to operate and suitable for application to water corporations.