Abstract: The behavior of strength loss of PLA fiber treated in the temperature of 30～90℃ and pH value of 3.85～11.8 was studied.The investigations show that,although the weak acidic condition of the liquor confer the relatively less damage to the PLA fiber,the significant damage still happened if treatment time was long enough.In the alkaline condition,with the increasing of pH value,temperature and time of treatment,the significantly increased strength loss of fiber will be present.