Environmental and water pollution caused by high-toxicity heavy metals is always a serious problem faced by human beings. As < 3 + >, Pb < 2 + > and Hg < 2 + > are environmental pollutants which have serious toxicity and are widely distributed, so that the environment and human beings can be seriously threatened even at low concentration. The standard of drinking water is strictly limited by the World Health Organization. Therefore, establishment of an efficient and sensitive analysis method capable of simultaneously detecting As < 3 + >, Pb < 2 + > and Hg < 2 + > is of great importance to the fields of environmental monitoring, food safety and the like. The invention provides a method capable of simultaneously detecting As < 3 + >, Pb < 2 + > and Hg < 2 + >, the method adopts a nanocapsule-nucleic acid biomolecule compound based on an exonuclease cyclic amplification technology, so that the As < 3 + >, Pb < 2 + > and Hg < 2 + > can be simultaneously detected, the detection sensitivity is remarkably improved on the premise of ensuring high specificity, and meanwhile, a wider linear detection range is obtained.