Abstract: A high-accuracy cuttings return monitoring device was developed to monitor and evaluate the hole cleanliness of horizontal wells, and to monitor the cutting return accurately. The compensation method for missing cuttings during a dumping period and the calculation method of the actual cuttings return volume were established for the monitoring device in two operation modes with the cuttings return data and the real-time data of engineering logging. A quantitative monitoring and evaluation technology for the hole cleaning of horizontal wells was developed depending on the results of the cuttings return rate and sloughing monitoring. This technology was applied in multiple horizontal shale gas wells in the Luzhou Block, Southern Sichuan, which enabled the real-time accurate monitoring of cuttings return volume and return rate in monitored well sections. It gave many early warnings regarding abnormal hole cleanliness, ensuring smooth drilling in horizontal sections. The proposed quantitative monitoring and evaluation technology for hole cleaning of horizontal wells provided a new technical means for monitoring the hole cleanliness of horizontal wells and preventing sticking and other complex risks.