The invention discloses a variable air volume (VAV) energy-saving control system for a central air-conditioner. The system comprises a master control cabinet, an air supply unit, air ducts, variable air volume (VAV) adjusting valves, indoor controllers and a monitoring system, the air supply unit comprises a frequency converter, a surface air cooler, a heater and a draft fan, a fresh air inlet provided with a fresh air valve and an air supply outlet are formed in an air supply duct, an air return duct is connected with the air supply duct through a fourway pipe provided with a proportion adjusting valve, and the monitoring system comprises an air supply pressure detector, a static pressure detector, an air return temperature detector, an indoor temperature detector and a carbon dioxide content detector. The control system can be set according to different users, local temperature can be changed, indoor air can be circulated continuously through the air return duct, the consumption amount of thermal energy or cold energy is reduced, and resource waste is decreased; in addition, according to the indoor carbon dioxide content detector, the master control cabinet adjusts the opening of the proportion adjusting valve and the opening of the fresh air valve, the fresh air inlet amount and air exhaust amount can be adjusted, the comfort degree of a user is raised, and meanwhile the energy dissipation is decreased to the greatest extent.