To discuss the effect about yield of synthetic D,L-lactide with potassium dihyrogen phosphate(PDP) diluents.The optimization process of synthetic D,L-lactide was selected by contrast experiments,optimization experiments and selective experiments of PD Pdiluents quantity,then D,L-lactide produced was analyzed by qualitative analysis and quantitative analysis.The yield of D,L-lactide was improved from 25.65% to about 40.00% when PD Pdiluents that was the most effective factor to affect yield was used from 4%to 6%,however,the rudimental PD Pcontent was only 0.012% and the content of D,L-lactide was above 99.40%.The yield of D,L-lactide was improved effectively with PD Pdiluents,and the D,L-lactide,which structure wasnot changed,could be polymerized into PLA and other polymers for enough content.