For a class of MIMO plants,using the idea of the high-frequency gain matrix K_p= L_2D_2S_2 factorization,the problem of design and analysis for MRAC is further investigated under the single assumption of known signs of the leading principal minors of K_p.By proving the L_p and L_(2δ)relationship properties between the input and the output and the multivariable swapping lemmas,the relation between all the signals in the closed-loop system and the normalized signal is obtained and the stability and tracking performance of the adaptive system is analyzed rigorously, the proof procedure being more compact. For a class of MIMO plants, using the idea of ​​the high-frequency gain matrix K_p = L_2D_2S_2 factorization, the problem of design and analysis for MRAC is further investigated under the single assumption of known signs of the leading principal minors of K_p.By proving the L_p and L_ (2δ) relationship properties between the input and the output and the multivariable swapping lemmas, the relation between all the signals in the closed-loop system and the normalized signal is obtained and the stability and tracking performance of the adaptive system is rigorously, the proof procedure being more compact.