Monolayer molybdenum disulfide is an ideal material for making various micro/nano components and flexible electronic devices. However, the strain of material caused by the environment is a key problem that cannot be avoided in practical applications, and the electronic structure of material will also change with the strain. In this paper, the effect of tensile strain on the photoelectric properties of monolayer MoS ₂is studied based on first principles and tensile tests after wet transfer. The results are obtained as follows. 1) Intrinsic monolayer MoS ₂is a direct bandgap semiconductor with a band gap of 1.68 eV, the highest peak of the absorption coefficient curve is nearly 10.92 eV, and a maximum absorption coefficient is 1.66 × 10 ⁵cm ^–1. 2) A small tensile strain (1%) will result in the transition from direct to indirect gap for monolayer MoS ₂. With the increase of strain, the feature of the indirect gap can be preserved but the gap decreases linearly. The gap will decrease to 0 eV when the tensile strain is 10%, and the absorption coefficient curve is red-shifted as a whole with strain. 3) The in-plane mode peak and the out-of-plane mode A _1gpeak in Raman spectra are re-dshifted with stretching by tensile test of wet-transferred monolayer MoS ₂, and the difference in peak frequency between the two peaks is maintained at about 18.6 cm ^–1. The strong emission peak of an exciton of monolayer MoS ₂is observed at 1.83 eV of the photoluminescenc spectrum. With the increase of tensile strain, the relative strength of the peak decreases and is linearly re-dshifted, which means that the band gap decreases linearly. It is consistent with the theoretical calculation result.