With the continuous increase of output power of double cladding fiber lasers, more effort is put into the researches of the technique of fiber laser beam combination, especially for incoherent laser beam combination because it is easier and with better system stability. Once high power output laser beam is achieved, there would be broad applications in industry, especially for manufacturing and material processing. The combination system's coupling efficiency plays an important role in determining the output power. Through theoretical analysis and numerical simulations, it has been proved that lower lateral off-set and higher grating period would be favorable, also an optimum spot radius exists which corresponds to a maximum value of coupling efficiency. Although lower focal length is helpful in improving the coupling efficiency, there is a contradiction that it makes a narrower fiber array width, which would limits the number of fiber lasers that could be utilized. Thus a moderate value of 20cm is chosen. Based on such optimized parameters, the beam quality M2 is around 2, also a method of two parallel gratings is introduced, which ensures the M2 factor to be around 1. Such combined fiber laser would be of great potential applications in manufacturing and material processing.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.