Laser diode bar (LDB) curvature, namely “smile” produced in the manufacturing and packaging process, affects the application of LDB in laser diode pumped solid-state laser and external cavity laser diode array. Using plano-convex cylindrical lens, “smile” can be corrected to some extent. By geometrical optics approach and ORIGIN software, “smile” correction was simulated and coincided with the experiment. The results show that this method works best if the “smile” is a parabolic curvature, and the relative correction value can be as high as 90%. “Smile” is corrected obviously by using suitable lens with short-focal length. Moreover, error can be further reduced by amending focal length of lens.