By its temperal characteristics, the error of the laser alignment could be divided into two parts, the random fluctuation with high frequencies and the slow drift. The former is originated from the atmospheric turbulence and can be alleviated by means of low-pass-filtering and/or many-time-averaging since its variance with time is unbiassed as well as random and of high frequencies. The latter results from the thermal deformation of the laser and of other related optical devices in the alignment system, and the change in the gradient of the atmosphere refraction index. Up to now, many methods to eliminate the error from the thermal deformation have been suggested and some satisfing tesults have achieved, however, there is no effective method to the error from the change in the gradient to be publicated. In this paper the authors present a method to synthetically alleviate the error from both the thermal deformation and the index gradient. See figure 1. The light beam from the laser is, first, collimated, then splitted into two parallel beams whose intensities are approximately equal. It is apparent that the drift of one beam caused by the thermal deformation is theoreticall identical to that of the other, and that the drift of one beam by the index gradient is approximately identical to that of the other when the distance between two beams is small enough. Therefore, if we choose any one of the two beams to be reference beam whose drift can be detected and the other to be alignment beam whose drift can be known through the former, the error of alignment caused by drift could be eliminated. In order to verify this a tentative experiment has been carried out.