A field irrigation experiment has been made in an instrumented loess landslide of  Heifangtai. Hydrological response and its effect on loess slope are analyzed based on monitoring data and numerical modeling. The result indicates that the groundwater table cannot be enhanced by short-term irrigation. However, the volumetric water content at shallow depths of the slopes increased rapidly, reducing the shear strength of loess and resulting in shallow failure at the margin of the platform. The numerical modeling results are consistent with the monitoring data, showing the numerical method can be used to simulate the hydrological response of the monitored site caused by irrigation.