The electrical and optical characteristics of GaN-based dual-wavelength light-emitting diodes (LEDs) with the specific design of various thick barriers are investigated numerically. The simulation results show that the thickness of barrier plays a regulatory role in emission spectrum of the dual-wavelength LED. The internal quantum efficiency droop is improved and the two peaks of spectrum become uniform due to the thickness of barriers gradually decreasing from the n-side to the p-side in a specific way. The balanced distribution of carrier concentration and the enhancement of electron confinement could be the major physical mechanism behind these improvements. It is also shown that the better optical performance is achieved at the large current injection level.