This paper describes a new active optical alignment method that is developed for the alignment of optical fibers to planar waveguide in order to improve the precision and efficiency of that. A new coupling mode, which is a polynomial function, is rebuilt by simplifying effect factors of the light field coupling process, such as angular offsets and line offsets. The optimum curve which is calculated to fit those sampling points by taking advantage of the least square method assists to locate the maximum coupling point of the alignment. Simulation results show that the alignment of two single mode fields is improved into 0.1μm precision with only 6 sampling points by the new method instead of 0.4μm offset with average 21.4 sample points by hill-climbing method. Using this alignment method, a fiber-to-waveguide, high-efficient coupling that provides higher accurate alignment with less sampling points is achieved.