Soil water content (SWC) is a key state variable in land-surface hydrological processes and the primary water source for vegetation, particularly in arid and semi-arid regions. However, long-term, multi-scale in situ measurements of deep SWC remain insufficient on the Loess Plateau of China (LPC), the world’s largest and deepest loess deposit area. To address this gap, the Loess-Obs network, a long-term multi-scale SWC observation system, was established on the LPC in 2004, covering five spatial scales including plot, hillslope, local-landscape, plateau-wide transect, and regional-survey scale. Here we present the long-term SWC profile dataset produced by this network, including continuous measurements (2004–2019) of four plots with distinct land uses, two hillslope transects of 300 m and 270 m (2004–2016), a 1340 m local-landscape transect spanning multiple hillslopes (2012–2013), an 860 km plateau-wide transect (2013–2016), and a regional survey of 243 points (2015). Volumetric SWC in the 0–5 m layer was measured at multiple depths using calibrated neutron probes (sampling frequency: weekly to monthly). The dataset also contains soil properties and the environmental attributes of each sampling point, including land use, terrain and climate. It supports the validation of SWC products, the development of upscaling methods, and studies of how deep soil water responds to land use and climate change.