The frequency-doubled and Q-switched quasi-cw YAG laser using KTP SHG crystals is a new pumping source for dye lasers. The performances of this’system sueh as efficiencies, optimum structure and output band widthwith different dyes and frequency selection elements are discussed. Considering the loss characters of the frequency selection elements and by obtaining the numerical solution of multi-wavelangth rate equation, the effects of beam round trips through frequency elements in dye laser cavity on the output linewidth are discussed. The calculation are in agreement with the experimental results.