According to various pumping styles, the laser output efficiency and optimal output coupling are different, and so do other parameters. Based on theory of rate equation, the optical-to-optical conversion efficiency of 511 nm copper vapor laser (CVL) transversely pumped Rh6G dye laser oscillator is studied. Result shows that the major reason of the difference of optical-to-optical conversion efficiency and output coupling between transverse pumping and longitudinal pumping is dye self-absorption. Experiments of transverse pumping have been done for various Rh6G concentration and output coupling mirror′s reflectivity, and the highest optical-to-optical conversion efficiency 8.2% was obtained. The relation between the efficiency and dye concentration and the reflectivity of output mirror was given. Experimental results show that the lower Rh6G concentration could reduce the influence of dye self-absorption on laser output efficiency, and meanwhile the optimal output coupling mirror′s reflectivity in transverse pumping is bigger than that in longitudinal pumping.