Numerical analysis is made on the H2/N2-air nonpremixed laminar counterflow diffusion flames with positive or negative stretch rate induced by locally sucking flow from fuel and air side. Adjusting the suction velocity forms typical three flames of flat shape and concave or convex curvature. Numerical computations taking into account detail chemical kinetics and multi-conponent diffusion makes it clear the effects of negative stretch rate on the flame structure and characteristics. In addition, the effects of preferential diffusion In relation to the flame curvature under the negative stretch are discussed. The results show that (1) Temperature increases with decreasing the stretch rate, and the tendency is the same even in the negative stretch rate. (2) H. concentration due to the preferential diffusion and excess enthalpy due to nonunity Lewis number effect becomes relatively significant with decreasing the stretch rate. This is one of the reasons of (1). (3) Temperature increasing due to the negative stretch rate depends on the flame curvature. (4) The maximum flame temperature cannot be rationlized by local stretch rate, and changes widely depending on the preferential diffusion in relation to flame curvature.