In order to study the hazardous elements of building materials, this paper analyzes the specific chemical composition of common building materials. The study of radioactive levels of different building materials may guide people to properly use building materials, so as to avoid health damage by radiation. This research adopts market survey, sample collection, treatment, determination and analysis, safety evaluation and others on building materials, investigates and analyzes the radioactive level of common building materials in Nanjing, and discusses reasons of high radioactive content of ceramic tiles. The experiment shows that in samples of measured building materials, the specific activity range of radionuclide content 226Ra of natural stones is 14.65-181.35Bq/kg, with an average value of 64Bq/kg. The radioactive levels of the measured natural stone samples meet type A standard of the national standard. It is concluded that the study of hazardous elements of building materials can guide people to use building materials reasonably and healthily.