It is necessary to lower the amount of meso-lactide formed in the thermal cracking process during polylactic acid production through lactide. This study chose catalyst concentration and depth of oligomer melts as governing factors through theoretical consideration and decided their order in rate equations by bench-scale continuous thermal cracking experiments. Orders of catalyst concentration and depth of oligomer melts are 4/3 and 1/2 in the rate equations of lactide formation and meso-lactide formation, respectively. Residence time of oligomer is proportional to the product of catalyst concentration to the -1/3 power and depth of oligomer melts to the 1/2 power. The ratio of meso-lactide formation to total lactide formation is proportional to the product of residence time and catalyst concentration to the 4/3 power. So, the ratio also becomes proportional to the product of catalyst concentration and the square root of the depth of oligomer melts. It is necessary to lower both catalyst concentration and depth of oligomer melts to lower the amount of meso-lactide formed.