A light wave is the emission wave of photons, and its propagation in a vacuum does not require any medium. Based on wave-particle duality of light, this paper proposes that the interference of light is caused by the wave characteristics of a single photon itself. A light wave is the cumulative expression of the individual movement of a single photon particle with the wave characteristics at different times. The double-slit interference of light requires neither two wave sources nor multiple photons to participate at the same time. Therefore, in the single photon double-slit interference experiment, a single photon can pass through one of the two slits in turn to achieve double-slit interference. There is no superposition principle in the single photon double-slit interference experiment, and a single photon cannot pass through two slits at the same time. Furthermore, a verification experiment to check the superposition principle of single photon double-slit interference is presented. A light shield is used to block one of two slits in turn to ensure that each single photon can only pass through one of the two slits separately. The verification experiment of single photon double-slit interference will expand people's understanding of the quantum world, and it is a new challenge to the superposition principle, Heisenberg uncertainty principle and quantum entanglement.