Abstract: A new algorithm of minimum enclosing rectangle based on the center-of-gravity principle, searching main axis method, was proposed. Using the center-of-gravity principle the initial positions and the rotating center of the horizontal axis and the vertical axis were obtained. The initial enclosing rectangle was determined by means of the horizontal axis. In the acute angle region between the horizontal axis and the vertical axis the enclosing rectangle was rotated until the enclosing rectangle of minimum area was found. This enclosing rectangle was just the optimization goals. The initial position of the main axis determined with the center-of-gravity principle was so efficient that region of search was shrunk and rotation count was reduced in the whole optimizing procedure. And since only the main axis which could be expressed by linear equation was rotated, calculating complexity was decreased remarkably and computation speed was increased effectively. Minimum enclosing rectangle of the object can be quickly found.