To solve the problems such as long production time and low selectivity in traditional methods for the preparation of glyoxylic acid from the oxidation of glyoxal,a modified synthesis by taking advantage of the microreactor was developed. 35％ nitric acid and 40％ glyoxal of a certain ratio were mixed in a T-micromixer,and the mixture was passed by the microchannel and the falling film microreactor for a certain residence time.The resultant solutions were mixed with nitric acid in a certain ratio again. After several cycles,the glyoxylic acid reaction solutions were obtained. Results showed that the conversion rate of glyoxal and the glyoxylic acid selectivity could reach 82％ and 95％ when the reaction was performed by a procedure with six cycles under the following conditions:initial mixture molar ratio of nitric acid ( 0. 13 mL/min) to glyoxal (0. 24 mL/min) of 0. 42:1,the flow rate of glyoxylic acid reaction solutions of 0. 24 mL/min,the flow rate of nitric acid of 0. 02 mL/min,the residence time and reaction temperature in the T-micromixer and microchannel of 2 min and 60 ℃, and the reaction temperature in the falling film microreactor of 90 ℃.