Abstract: Currently, the topological behavior of materials is a hot topic in condensed matter physics. As a new class of topological quantum states, Weyl semimetals have attracted extensive interest. Taking the pyrochlore iridatesA₂Ir₂O₇ (A=Y or rare earth element) as an example, we discuss the novel properties of Weyl semimetals. Their Weyl nodes are robust, they have special surface states in the form of Fermi arcs, the anomalous Hall effect is proportional to the separation between the Weyl nodes, and they have novel transport properties. We also discuss some materials predicted to beWeyl semimetals, and recent experimental progress.