Abstract: Because of electron density gradients, refraction will occur when x rays propagate in plasmas. Refraction tends to go direct the x rays out of high density regions, shortening the distance that x rays can travel within the plasmas, and limiting the amplification thereby. In thick target, refraction is more serious. Double- targets coupling design can lessen refraction .In this paper, we suppose that the density and gain profiles within the plasma are linear and find that refraction introduces a loss term to the laser amplification.Theoretical simulations for x-rays refraction in the gain region are shown.