Concrete would be deteriorated by various factors in severe environment. Chemical erosion of concrete in acidity environment is one of important deterioration mechanism. It is not clarified, however, how chemical characteristic change affects mechanical characteristics. Meanwhile, a meso-scale approach in which both aggregate and mortar can be modeled is on the verge of becoming possible to apply to such durability problems. In this paper, the relationships between chemical characteristic change (amount of CH and CSH) and mechanical characteristic change are examined experimentally and then the mechanical behavior is simulated by Rigid Body Spring Method which is a typical meso-scale analysis. In particular, meso-scale constitutive laws are obtained from the bending tests of deteriorated mortar specimens after immersion test. Finally the applicability and availability of the analysis with the developed constitutive laws are discussed based on comparison with experimental.