Indoor air quality (IAQ) is affected by several factors and the level of indoor air quality is a fuzzy idea, thus how to assess indoor air quality according to these single indexes is an important problem that it is time to solve. The assessment method should express the integrative influence of these factors on indoor air quality. Based on the analysis of grey incidence, which is an important part of grey system theory, this paper assesses indoor air quality by the abundant information provided by grey incidence matrix. According to the analysis and comparison with other methods, it is clear that the grey assessment is an ideal method of assessing concerned with several parameters because the procedure is simple and the outcome is credible.