This paper presents, method of moments based analysis of broad-wall longitudinal slots array antenna using Multiple Cavity Modeling Technique (MCMT). Theoretical data for reflection coefficient, transmission coefficient, resonance length and resonance conductance have been obtained for two slots in two different waveguide. The theoretical data have been compared with Ansoft HFSS's simulated data to validate the proposed method. The excellent agreement obtained between the results demonstrates that the proposed method is able to accurately and efficiently solve complex reflection coefficients and transmission coefficients for different slot parameters.