A 1.3 μm high-speed, double-junction cascaded quantum-dot (QD) active-region vertical-cavity surface-emitting laser (VCSEL) is designed using PICS 3D simulation software. The impact of the tunnel-junction cascaded QD active region on the high-speed performance of the VCSEL is investigated. The tunnel-junction cascade structure effectively enhances both the output power and the small-signal modulation bandwidth of the QD VCSEL. Under continuous-wave conditions, a double-junction cascaded VCSEL not only reduces the threshold carrier density but also improves the quantum-well differential gain compared with a single-junction QD VCSEL. The results show that doubling the number of active regions increases the modulation bandwidth, decreases the threshold current, and exponentially enhances the output power and slope efficiency. For a double-junction cascaded QD VCSEL with a 12 μm oxide aperture at a current of 10 mA, the small-signal modulation bandwidths at 25 °C and 85 °C are 28.0 GHz and 17.8 GHz, respectively. This represents improvements of 16.67 % and 22.76% over single-junction QD VCSEL. The output power of the double-junction cascaded QD VCSEL reaches 17.3 mW at room temperature with an injection current of 10 mA. Further reduction of the number of logarithmic DBRs on top of the double-junction cascaded QD VCSEL increases the small-signal modulation bandwidths to 29.6 GHz and 18.0 GHz at 25 ℃ and 85 ℃, respectively. The designed double-junction cascaded 1.3 μm QD VCSEL provides data and theoretical support for epitaxial-material preparation.