Based on topological horseshoe map theory, the paper analyses the existence of topological horseshoe in a 3-D four-wing chaotic system. As the chaotic system is continuous, the paper first choses a Poincaré section, then under which defines a first return Poincaré map. A conclusion that the Poincaré map is semi-conjugate to 2-shift map can be obtained by utilizing computer-assisted verification, showing that the topological entropy of the 3-D four-wing system is larger than or equal to ln2, which further verifies the chaotic characteristic of the system.