In this study, we propose a scheme to generate tunable and broadband two-channel optical frequency comb (OFC) based on a gain-switched 850 nm vertical-cavity surface-emitting laser (850 nm-VCSEL) under orthogonal optical injection. In addition, the influences of some operation parameters on the performances of the generated OFC are numerically investigated. For developing this scheme, an 850 nm-VCSEL is modulated using a large signal current and is subsequently driven into a gain-switching state. In this case, the Y polarization component of the laser oscillates and behaves in a periodic pulse state, whereas the X polarization component is suppressed. Therefore, a one-channel OFC is generated in the Y polarization direction (Y-OFC). The X polarization component of the gain-switched 850 nm-VCSEL can be oscillated to achieve a periodic pulse state with a spectral intensity equivalent to that of the Y polarization component by introducing optical injection polarizing along the X direction (orthogonal optical injection). Thus, a two-channel OFC can be obtained. The simulated results are obtained based on an 850 nm-VCSEL under current modulation with a modulation depth of m=0.75 and a modulation frequency of fm=4.2 GHz as well as orthogonal optical injection with frequency detuning of Δv=10.0 GHz; these results indicate that a two-channel OFC having bandwidths of greater than 105.0 GHz with an amplitude variation of less than 10 dB can be obtained under the optimized injected field amplitude Einj. Subsequently, the ranges of Einj and Δv are determined by examining the optical spectra of the X and Y polarization component outputs obtained from the gain-switched 850 nm-VCSEL subjected to orthogonal optical injection for obtaining a two-channel OFC. Finally, the tunability of comb spacing is demonstrated by analyzing the OFC performance under different values of fm.