The quantum interference effect in single-molecule devices is a phenomenon in which electrons are coherently transported through different frontier molecular orbital with multiple energy levels the interference will occur between different energy levels. This phenomenon leads to an increment or decrement in the probability of electron transmission in the electrical transport of the single-molecule device, and it is manifested in the experiment as an increase or decrease in the conductance value of the single-molecule device. In recent years, the use of quantum interference effects to control the electron transport in single-molecule devices has been proved to be an effective method, such as single-molecule switches, single-molecule thermoelectric devices, and single-molecule spintronic devices. This article introduces the related theories of quantum interference effects, early experimental observations, and their regulatory role on single-molecule devices.