The hydroxyl terminated polylactic acid was synthesized from lactic acid and 1,4-butanediol through solution polymerization combined with melt polycondensation catalyzed by stannous chloride and p-toluenesulfonic acid. High molecular weight polylactic acid was prepared by chain extension of hydroxyl terminated polylactic acid using hexyl dichloride as a environmentally friendly chain extender. The polymer was characterized by means of IR，1HNMR，and TGA. The results showed that the optimum response technological conditions is that the dosage of the hexyl dichloride is nCOCl: nOH of 1:1, and the deacid reagent pyridine is nPy: nHDC of 4:1，reacting for 45 min at 160℃，The Mη of chain extension product was 70825 and was 2.3 times higher than before chain extension.