The influence of temperature and time of dry-heat and wet-heat processing on the tensile property of the PLA fibers was investigated. The results indicate that as the temperature and time increase, the tensile strength of the fibers gradually decreases. When the temperature is above 100 °C or time over 20 minutes, the dry-heat treatment results in significant decrease on tensile property of the fibers. In the wet-heat treatment, the strength of PLA fibers is influenced by the treatment time, temperature and pH value. The acid-resistant property of PLA fibers is better than the resistance to alkali. Under weak acid condition, the performance of PLA fiber is relatively steady. But the fibers under alkali condition over 100°C are hydrolyzed into pieces and the force losses nearly completely. Moreover, the oxidant and reducing agent also impart the tensile property of PLA fibers. The concentration of H2O2 no more than 5g/L is appropriate, whereas the lower concentration of Na2S2O4 is proper.