The source, composition, formation and hazard of haze and PM2.5 were introduced. The development of new methodology for the analysis of PM2.5 is important for the understanding of the hazards, the study of the biologic effects, and the finding of the source of haze and PM2.5. The efficient utilization of clean energy, the post-processing of effluents, and "carbon trading" may become the breakthrough points to solve haze and PM2.5 related issues.