The stability of solutions in the problem of architecture design for software system is examined in the paper with taking to the account the quality attributes for software system, obtained with Analytical Hierarchic Process. For this purpose, for different values of elements' inconsistencies in the matrix of pairwise comparisons, given as random numbers, were compared inconsistency criteria of decision for optimization problem obtained with a classical and with a modified Analytical Hierarchic Process. We also examined the sensitivity of solutions for selection of optimal architecture to the inconsistencies of matrix of pairwise comparisons, and to the errors in determination of priority indices for quality criteria. Obtained results showed the advantages of modified Analytical Hierarchic Process, and they showed the influence of solution stability to the inconsistency of pairwise comparisons on the correctness of results of architecture optimization for software system.