Based on the theory of light transmission matrix, the light spot radius and relative intensity distribution of metamaterials in ring cavity were studied. The results show that the spot radius becomes larger and the central relative intensity is weaker in meridian plane and sagittal plane when wave propagates a circle by choosing the internal negative refractive index materials as a starting position. The spot radius reduces quickly after leaving the negative materials, then reaches the maximum again at the surface of the concave mirrors, but it is far less than that of the inside negative materials. When the transmission start point of light is away from the concave mirror, the spot radius decreases, and attains the minimum at the center of the two plane mirrors, thus the relative center intensity reaches maximum value. On basis of this theory, the influence of negative material length and the refractive index on beam waist radius were analyzed. It is found that the medium length affects little on the waist radius in meridian plane and sagittal plane. However, refractive index has much influence on the waist radius of the internal negative materials, the beam waist radius decayed quickly when the refractive index changes from -5 to -1, but the spot radius is less affected at the center of two flat mirrors, where the two waist radius curves are near to the horizontal lines.