Duct leak check is a new item in the National Code-GB 80243-97 for construction and acceptance of ventilation and air conditioning works. The main methods for duct leak check unit with throttling device, used in acceptance of ventilation and air conditioning works is introduced in the paper. Generally the duct system leakage rate is an important element in quality management and energy reduction. An experimental unit with standard orifice plate has been designed and installed with some improvement measures such as test fluepressure control and automatic wall pressure tapping.