Abstract: Based on the real-time observation data obtained from Yutai Marine Ranch off Weihai in August 2020, as well as the cruise observations, the current study investigated the diurnal variation characteristics of dissolved oxygen (DO) in the bottom layer, with a discussion about its influencing factors. The result indicated that the average diurnal variation of DO concentration in the bottom layer ranged from 4.02 mg/L to 4.45 mg/L, presenting a unimodal structure, but the hourly monthly standard deviation of DO concentration had a few peaks. The everyday occurrence time of the peak of the DO concentration was delayed with the date and the maximum DO concentration mostly appeared at 12. The saturated DO concentration was mainly affected by temperature, and its amplitude of daily variation was only 1/10 of the DO concentration’s amplitude. The average diurnal variation of apparent oxygen utilization ranged from 2.75 mg/L to 3.21 mg/L, so the bottom layer was always in an unsaturated state. The diurnal variation of DO concentration wasn’t directly controlled by temperature. However, the rise and fall of sea surface caused by tide may change the intensity of net solar radiation reaching the bottom layer, so that the photosynthesis altered, and the diurnal variation of DO concentration varied. Moreover, the advection transport also had an impact on the diurnal variation of the DO concentration. The result of this paper can provide a reference for further research on the marine ecological environment and its influence mechanism, which features higher ecological and economic worth.