This paper investigates the spectrum theory of a self-aligned InP/AlGaInP bilayer quantum dot laser fabricated by organic-metallic vapor phase epitaxy. In the fabrica-tion process, dipole size distribution of quantum dots (groups of small and large quantum dots) has been identi-fied. Therefore, a model based on song equations and considering the superposition of two heterogeneous groups of quantum dots has been proposed. The total output power and power spectral density (PSD) of the fabricated quantum dot laser at room temperature are determined theoretically. Also, the output spectrum is divided into the sum of two Gaussian (super-Gaussian) curves correspond-ing to the groups of small and large quantum dots. The peak power spectral density (PSD) and spectral width of each group are extracted and their dependence on the in-jection current density is investigated. The results show that the peak corresponding to large quantum dots domi-nates at low currents, while at high currents the peak corre-sponding to small quantum dots dominates and its spec-tral width decreases. This behavior is attributed to the satu-ration of energy levels of large quantum dots due to their relatively long radiative lifetimes.