Abstract: By analyzing and synthesizing the advantages and disadvantages of the two generally used design methods for slotted waveguide antenna array (the esperimentally measuring method and the theoretically computing method), the idea and practical method are presented in this Paper, that the aetive admittance and the resonant length of waveguide slot in simulated array environment are computed by theoretically analyzing method. Thus, it can not only leave out the machining of the iest components and the procedure of measurement, but also make full use of the characteristic that theoretically computing method is suitable for the analyzing the small slotted waveguide antenna arrays. So the works for design a slotted waveguide antenna array can be reduced greatly.