Unstable beam direction of the laser is caused by many factors. The important one is that the tilt of reflector in resonator is not stable. This article studied the way to stabilize the beam direction of a He-Ne laser by stabilizing the angle of the resonator. First the eigen-modes of confocal cavity in which the reflector is symmetrically tilted have been calculated, and the shift of the laser beam in direction for this cavity has been discussed. For the flat-concave cavity with stabilized beam direction, R/L = 1 has been found out theoretically by means of equivalence of oonfooal and flat-concave cavity. In consideration of the stable region for tho flat-conoave cavity and the stability of laser intensity should be larger. The He-No laser of β=1.2 has been mado, for which the directional stability is evidently better.