The terminal cooling load distribution and pipe network structure of the air-conditioning system are the key factors that influence its control stability and reliability. An exact mathematical model of pipe network hydraulic characteristics was built in this paper based on a directreturn chilled water system, in which the regulation characteristics of bypass loop was considered in detail. The influence of pipe network hydraulic characteristics and energy consumption characteristics on pressure difference setting value of bypass loop were studied in detail, and the hydraulic characteristics in different running conditions were also studied. This paper focused on the influence of static stability and control quality on variable pressure difference control system by checkpoint of pressure difference feedback signal. The research shows that reasonable adjustment in control target value and setting value of bypass control valve are the key factors to achieve efficiency and stable operation.