Molybdenum disulfide (MoS$_2$) has attracted interest owing to its strain-tuned electronic and optical properties, making it a promising candidate for applications in strain engineering devices. In this study, we investigate the effect of uniaxial strain on the electronic properties of MoS$_2$ monolayer using first-principles calculations. Results show that a crossover of the K-K direct to -K indirect bandgap transitions occur at a strain of 1.743%. Moreover, a strong correlation is observed between the modified bandgap and the density of states (DOS) of the Mo-4d and S-3p orbitals at the valence band maximum and conduction band minimum. The uniaxial strain-tuned interatomic distance along the a-crystallographic axis does not only alter the bandgap at different rates but also affects the DOS of the Mo-4d orbital and possible electronic transitions. This study clarifies the mechanism of the electronic structural modification of two-dimensional MoS2 monolayer, which may affect intervalley transitions.