Microporous aeration is extensively used, and oxygen mass transfer during aeration has a direct impact on water remediation. Nevertheless, the research on the mechanism of oxygen mass transfer in microporous aeration is lacking. This study aimed to explore the variation in oxygen mass transfer from the bubble-movement flow-field in a microporous aeration system. Then, the characteristic parameters of oxygen mass transfer and bubble movement (by particle image velocimetry) were determined under different aeration rates. Results showed that aeration rates were significantly positively correlated with bubble number (R = 0.98), bubble-movement velocity, total oxygen-mass-transfer coefficient (KLa), and oxygenation capacity (R2 = 0.98, 0.98). This finding indicated that the increase in bubble number and bubble-movement speed accelerated the oxygen mass transfer and improved oxygenation performance and KLa . Moreover, a significant positive correlation existed between aeration amount and average Sauter diameter (R>0.97), but a significant negative correlation existed between aeration amount and specific bubble surface area (R<-0.98). Thus, increased aeration amount led to increased average bubble Sauter diameter. These phenomena further led to decreased specific bubble surface area and EA. Overall, these results can guide the research on oxygen-mass-transfer mechanism from the perspective of bubble-movement flow-field.