The invention relates to a melt / 
solid state polycondensation preparation method for 
polylactic acid, which mainly solves the problems of long reaction time, difficult 
continuous production or high cost in the prior art. The method comprises the following steps of: 1) performing a 
dehydration oligomerization reaction of 
lactic acid at the temperature of between 100 and 160 DEG C under the absolute pressure of between 6,000 and 25,000 Pa and under the action of a catalyst A for 0.5 to 5 hours first, and continuing the ehydration oligomerization reaction at the temperature of between of 120 and 180 DEG C under the absolute pressure of between 200 and 1,500 Pa and under the action of the catalyst A for 0.5 to 5 hours to generate a product I; 2) performing a melt 
polycondensation reaction of the product I at the 
reaction temperature of between 150 and 200 DEG C under the absolute pressure of between 30 and 600 Pa and under the action of a catalyst B for 0.5 to 15 hours to generate a 
polylactic acid prepolymer and 
lactide serving as a by-product, and refluxing the 
lactide to a reaction mixture at the 
reflux temperature of between 70 and 95 DEG C; 3) 
pelletizing the 
polylactic acid prepolymer obtained in the step 2), and crystallizing in an 
inertia airflow at the temperature of between 50 and 130 DEG C for 0.5 to 10 hours; and 4) performing a 
solid state 
polycondensation reaction of the polylactic acid 
prepolymer processed in the step 3) in the 
inertia airflow at the temperature of between 120 and 170 DEG C for 5 to 40 hours to obtain the polylactic acid. The technical scheme of the invention better solves the problem, and can be used for the industrial production of the polylactic acid.