Test investigations show that the reinforcement scheme with adding diagonal and rhombic bars to traditional reinforcement in the foundation is an ideal way, for the seismic performance of small span-to depth ratio coupling beams with this scheme is better than that of traditional reinforcement. Because the regions in the small aspect ratio coupling beam belong to D-regions, in which the Bernoulli hypothesis of plane strain distribution is invalid, the traditional bending theory can not be used. This paper simulates the coupling beam through non-linear finite element analysis program, and contrasts the analysis result of the bar's stress distribution with test result. The contrast results confirm that it is a valid way to analyse the bar's stress distribution in this coupling beam through non-linear finite element analysis program.