Abstract: Pure copper and its composites reinforced with different volume fractions of AlN particles were prepared by powder metallurgy.The thermal expansion behavior of composites was studied from 50 ℃ to 550 ℃.The temperature range of matrix plastic deforming caused by thermal stresses was calculated with mises yield rule.The soft temperature of AlNp/Cu after plastic deforming was measured.The soft temperature of copper matrix could be effectively improved and thermal expansion of copper matrix could be effectively restrained by the AlN particles;Under the action of porosity and thermal stresses,the thermal expansion curve of AlNp/Cu composites became non-linear with the particle volume contents increasing to a certain extent.The composites exhibited positive residual strain when cooled down from the peak temperature to room temperature because of the copper matrix plastic deformation caused by thermal stresses.