To examine the fine-scale structure and evolution of the low-level wind field at a plateau valley airport under different weather conditions, this study analyzes a two-stage wind field event at Xining Caojiapu Airport on 8 April 2022. The analysis uses data from several scanning modes of a three-dimensional Doppler wind lidar (DWL), together with an automatic weather observation system (AWOS), sounding data, and the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5). The results show that: (1) From 13:25 to 13:45 BJT, downward momentum transport produced low-level wind shear. Under an upper-level jet, post-trough northwesterly flow, and stronger afternoon mixing in the boundary layer, west-northwesterly winds aloft descended and entered the runway area from west to east. Runway 11 responded about 1–2 min before Runway 29. The maximum wind vector difference between the runway ends was 9.42 m s⁻¹, and the maximum wind speed component difference along the glide path was 9.02 m s⁻¹. (2) From 20:15 to 20:35 BJT, the low-level wind field adjusted as a cold front moved into the airport. Strong easterly flow advanced westward from the eastern side as a shallow wedge, with local shear along its upper boundary. Runway 29 responded before Runway 11. The corresponding maximum differences at the runway ends and along the glide path were 6.44 and 4.01 m s⁻¹. (3) The two stages differed in airflow direction, the evolution of the shear interface, and the order of response at the runway ends. Combining the DWL scanning modes with AWOS observations gave a clearer view of the descending strong wind layer, the advance of low-level airflow, local shear, and wind changes over the runway and approach path. This case provides a reference for low-level wind monitoring and operational risk assessment at plateau valley airports.