Based on the nonreciprocal property of Faraday effect, we investigate the light output from optical reflection cavity filled with Faraday optical rotation medium. It is shown that such a reflection cavity has the enhancement effect of megneto-optical rotation （MOR）. Base on this phenomenon, a detection method for small rotation angle is proposed, and the characteristics of MOR enhancment device is analyzed. The relations between the detection sensitivity and the factors of reflection, absorption and rotation angle are discussed analytically and simulated. The problems discussed include the angular working point, the measuring range, and the theoretical limitation of detection sensitivity. Under the condition of small angle approximation, the output intensity is proportional to the square of the rotation angle, and increses with the nise of device reflectivity. The angular working point and measuring range decrease monotoniccally with the increase of reflectivity and the drop of the absorption. The limiting value of relative sensitivity is 78.49. The results indicate that the MOR enhancement device can be applied to MOR detection of microfluidic system and miniaturization of MOR instruments.