MoS₂, as a typical material of two-dimensional semiconductor transition metal chalcogenides, has excellent physical properties such as tunable band gap. Therefore, MoS₂ moiré superlattice is an ideal system for investigating the electron transport in condensed matter and the design of optoelectronic devices. On the other hand, interlayer conductance serves as a significant indicator for analyzing coupling effects in moiré superlattice. Here, in order to clarify the influence of tunable band gap on the interlayer conductance, we develop a tunneling theory for calculating the interlayer conductance of MoS₂ moiré superlattices by using optical methods in diffraction physics. In this theory, the electron tunneling can be considered as the diffraction of electron waves by the periodic gratings. Accordingly, the influences of the periodicity of MoS₂ moiré superlattices and the coherence of the tunneling electrons can be well included in the theory. In addition, the effect of the tunable band gap of MoS₂ is taken into account. According to the theory, we investigate the properties of the interlayer conductance of MoS₂ moiré superlattice. The theoretical results show that due to the diffraction effect, there exist two partial waves of the tunneling electron at the interface, which can resonate with the interface potential. Accordingly, the interlayer conductance curves exhibit a double-peak structure. Furthermore, we analyze the influences of the tunneling layer and the metal electrodes on the interlayer conductance: the thickness of the upper MoS₂ lattice affects the peak and the lower one primarily influences the background. The coherence of tunneling electrons will be enhanced when the parameter of interface potential strength increases. The chemical potential of the metal electrode mainly affects the properties of the peak, and the influence is more significant than that in graphite moiré superlattice.