Glycolide has been synthesized by depolycondensation of the low molecular weight polyglycolic acid (PGA), and the oligomers was prepared by polycondensation of glycolic acid(GA), which is the by-product of the coal chemical industry. It was found that heating rate has a great influence on the yield of glycolide. The effects of reaction conditions on the yield of glycolide have been investigated and the optimized conditions are as follows: the polymerization temperature is 180 ℃, Sb2O3 was discovered to be the best catalyst and the centration is 0.75wt%, the depolymerization temperature is 290 ℃ and rising to it at a rate of 15 ℃/min. Under the optimized conditions, the yield of crude product of glycolide reaches up to 87.5wt%, the purity is higher than 99.9% after recrystallization and the yield is 78.0%. The glycolide with high purity was identified by infrared spectroscopy, hydrogenspectrum of nuclear magnetic resonance.