Abstract: As the "blood" of drilling engineering in petroleum industry, drilling fluid plays a very important role in the process of oil and gas exploration and development. At the job site, drilling fluid is also an important source of drilling wastewater. With the further promotion of cleaner production and the improvement of environmental awareness, the requirements of drilling wastewater and its treatment on the job site have become more and more stringent. In response to the characteristics of good stability, high chemical oxygen demand and difficult degradation of drilling wastewater, micro-nano bubbles were used to improve gas utilization and mass transfer effect, and ozone gas was used to degrade high-difficulty and high-concentration organic matter. The aim was to solve the problems of high chromaticity and high COD of drilling wastewater. The indoor simulation experiment showed that after pretreatment, by using ozone micro-nano bubble technology, COD decreased from 47 328 mg/L to 131 mg/L, with the removal rate of 99.7%, and TOC decreased from 15 146 mg/L to 65.2 mg/L, with the removal rate of 99.6%. The removal rates of COD and TOC could reach more than 99.5%, and the ozone micro-nano bubble technology had a significant removal effect on high chromaticity and high COD. The experiment also showed that the flocculation precipitation and Fenton process combined with ozone micro-nano bubble technology could reduce the amount of ozone added, thereby reducing the investment and operating costs, making it an economical and efficient treatment method.