Abstract: ObjectiveTo survey the indoor air pollution by central air conditioning system in summer and winter in the public places in Zhoushan. MethodsTwenty two institutions with central air conditioning system were selected. Thirty-two samplings were taken in summer and winter to detect the contents of CO, CO2, PMsub10/sub, volume of fresh air, total bacterial count in the areas benefiting from the systems, the volume of dust, total fungus count, total bacterial count, - hemolytic streptococcus，Legionella in the ventilation pipes and the total counts of bacteria and fungus in the outlets of ventilation pipe. The effect of cleaning of central air conditioning systems was also evaluated. ResultsThe acceptance rate of total bacterial count and total fungus count for the outlet were 37.50%（12/32）, 46.88%（15/32）respectively. The acceptance rate of total fungus count and total bacterial count for ventilation pipes were 65.63%（21/32）, 81.25%（26/32） respectively. The acceptance rate for pipe dust detection was 81.25%（26/32）. The acceptance rate for fresh air volume detection was 62.5%（20/32）. The acceptance rate for CO2 content was 81.25 %（26/32）, and the rates for CO, PMsub10/sub contents and bacterial count in air were 100%（32/32）. The acceptance rate of Legionella detection was 35.71% (20/56). There were significant differences on temperature (I/Isup2/sup = 4.57), COsub2/sub content (I /Isup2/sup = 5.74), fresh air volume (I/Isup2/sup = 4.10) in summer and in winter, and there was significant difference (It/I=2.25) on the pipe dust volume for the pipes which hand been cleaned or not. ConclusionThe central air conditioning systems have made indoor air pollution at certain degree in Zhoushan, which was a threat to people s health. To improve indoor air quality, it is necessary to strengthen the management of the air conditioning systems, and conduct cleaning and disinfection of ventilation pipes regularly, thus the transmission route of respiratory disease could be interrupted and the people in the public places could be protected.