The quantum dot-cavity system was investigated using a quantum master equation that took incoherent pumping, stimulated emission and pure dephasing into consideration, and analytical emission spectra at cavity and dot were presented. The theoretical analysis results show that the pure dephasing shifts the emission intensity towards the cavity frequency in non-resonant coupling system and thus can be a very good explanation of the non-resonantly coupled cavity effective emission effect. In order to further study the application of pure dephasing in the quantum dot-cavity coupled systems, the effective quantum dot-cavity coupling rate and the efficiency of the single photon source for detuned systems were introduced, and good cavity and bad ragime were able to be defined through comparing the effective quantum dot-cavity coupling rate and the cavity decay rate. Influence of the pure dephasing on the efective coupling rate and the efficiency of the single photon source were investigated in resonance and detuning selected two set of theoretical parameters according to the experimental data. The results show that the pure dephasing can increase the efftive quantum dot-cavity coupling and the efficiency of single photon source for detuned system and thus may make a transition from bad cavity to good cavity ragime; a set of parameters having larger coupling efficiency in a certain range can meet good cavity ragime that its single photon sources efficiency is obviously better than the other set. Compared with bad cavity regime laser in non-resonant coupling system, the good cavity regime is a necessary condition to achieve single quantum dot lasers; the Fano function shows no evidence of a maximum in the non-resonant coupling system and thus there is no laser threshold in this system.