Groundwater is an important water resource for the ecological restoration and the life and production of the inhabitants of the Loess hilly region. A quantitative exploration of groundwater recharge mechanism and the spatial-temporal variation pattern is the key for an effective evaluation of groundwater resources in this region. Based on a Bayesian model and a Sinusoidal model, the spatial-temporal distribution pattern of the water transmission time and the groundwater recharge ratio were investigated. The results showed that the transmission time of groundwater by precipitation and surface water were 443.16 d and 64.58 d, respectively, which yielded a recharge ratio of 29.22% and 70.78%, respectively. Surface water was the main recharge source of groundwater in this region. The values of the groundwater recharge ratio by precipitation in the rainy season and dry season were 32.83% and 25.60%, respectively. Groundwater recharge mainly occurred during the rainy season. From upstream to downstream of the small watershed, the groundwater recharge ratio by precipitation increased gradually, while the groundwater recharge ratio by surface water decreased. The spatial characteristics of groundwater recharge ratio were all nonetheless not obvious. Groundwater recharge mainly took place in the upstream region of the watershed, while the discharge took place in the downstream area. Groundwater recharge occurred mostly through a combination of piston flow and preferential flow. The findings of this study could provide a reference for the development, the utilisation and the protection of groundwater resources in small watershed in the Loess Hilly region.