In this paper, a new window model for designing FIR digital filter is suggested. For the suggested model, two parameters are established and their effects to the characteristics of filter are analyzed. As a result, one of these parameters improves the characteristics of the transient region but degenerates those of peak sidelobe a little bit, and the other contrasts the characteristics with the former. These effects of parameters give selectivity to design window. Therefore the new suggested window model gives flexibility to filter design and its improved characteristics is comfirmed by simulation.