Spherical cameras are suitable for all-round 3D measurement due to their wide field of view. When performing 3D measurement using binocular spherical stereo, the areas in the epipolar directions cannot be reconstructed accurately due to the low measurement confidence in the epipolar direction. By adding one more spherical camera, perpendicular to the epipolar direction, to the binocular spherical stereo to form a trinocular spherical stereo, all-round 3D measurement can be achieved. In this paper, we propose a method to improve the 3D measurement accuracy by minimizing the overall reprojection error. Effectiveness of the proposed method is verified through experiments.