The influences of processing conditions on the mechanical performances of poly(trimethylene terephthalate)/acrylonitrile-styrene-acrylic copolymer (PTT/ASA) blends were investigated in detail. By changing the molding temperatures and pressure-held times, the testing samples were prepared by injection molding method and their crystallinity, impact and tensile strength were characterized by differential scanning calorimetry, universal material tester and impact tester. The results suggest that high molding temperatures can increase the crystallinity of the blends, and then increase the impact and tensile strength of the blends. By extending pressure-held times, the crystallinity of blends increases, and the tensile strength increases gradually. The blends with different ASA contents have different changing rule of mechanical performance with varied molding temperatures on pressure-held time.