Abstract: The concave configuration represents a prevalent and pivotal structural form within hydrophobic materials. Comprehending the slip velocity characteristics associated with concave surfaces carries profound implications for the design of these materials. This investigation employs the Discrete Unified Gas-Kinetic Scheme (DUGKS) to simulate the low-speed, two-dimensional concave flow within the Knudsen number range spanning from 0.01 to 0.5. The numerical simulation results reveal a noteworthy variation in slip velocity patterns in relation to the Knudsen number. As the concave size decreases (Kn > 0.3), the slip velocity within the concave region is lower than that on a smooth wall. Conversely, as the concave size increases (Kn < 0.2), the slip velocity exceeds that of a smooth wall. Additionally, there are discernible jumps in the statistically-averaged slip velocity at the cavity's boundaries, which become more pronounced with an increasing Knudsen number, suggesting that the Knudsen number should not exceed 0.3 when designing hydrophobic microstructures.