The article divided into five parts. The first part is an introduction. One of the most important subjects in museum is the conservation of cultural relics. Great importance to the museum environment should been attached. It is necessary to study how fast things in the museum change and what causes these changes, and to erect a framework of preventive conservation in museum environment standard. The second part is an investigation report of environment at principal museums in the east and southwest of China (Shanghai museum, Chongqing museum and Guangdong provincial museum). The climate condition of these museums is warm and moisture, besides, the air pollution is due to the development of industrial and vehicle. The results of examination showed that the concentrations of sulfur dioxide, nitrogen oxides are higher. The air pollution in these museums is serious. Museums are generally situated in the urban area in China, so the present situation of air pollution is the same. The quality of museum environment is directly related with the conservation. The third part, the potential damaging effects of temperature, relative humidity, light (visible and UV radiation) and air pollution are discussed respectively. A change of relative humidity causes changes in size and shape of moisture – containing materials. High relative humidity causes mould to flourish and metals to corrode. The light is much more potential than heat (temperature) in the museum. The chief materials to suffer from sulphur dioxide pollution are paper, silk, textiles, dyes, leather, iron, stone and etc. Since the nitrogen dioxide dissolves in water eventually to form nitric acid, an acid as strong as sulphuric acid and on the top of that an oxidising agent, all the troubles that sulphur dioxide gives us can been expected. Nitrogen dioxide attacks dyestuffs containing amine groups, indigo is such a dye. When multi damaging factors co-existing, the rate of deterioration is speeding. There is synergistic effect among the presence of moisture, light, gaseous pollutants and particulate matter. In the fourth part, the quality standard of museum environment (temperature, relative humidity, gaseous pollutants, particulate matter and etc) has been formulated. The quality standard divided in three classes. According to the situation (cost, technology, degree of susceptibility of materials and etc.), it is necessary to carry out the quality standard step by step and then to attain the best possible environmental conditions. In order to minimize the damage of materials as low as possible and to attain the quality standard, it is necessary to control and examine the museum environment. The control methods and the examination technique were recommended in the fifth part.