This dataset contains multi-site, multi-constellation and multi-frequency GNSS observations collected at 11 fixed monitoring sites and three synchronized monitoring sites. The dataset includes raw UBX messages, processed satellite–time observation matrices, site metadata. The fixed-site observations cover complete satellite visibility cycles under different local propagation environments, including open-sky, building-blocked, vegetation-blocked and mixed-blockage conditions. The synchronized observations support comparative analysis under the same time, satellite geometry and signal frequency conditions. The dataset can be used for ionospheric sensing, TEC retrieval, propagation-environment sensing, LOS/NLOS discrimination, local blockage-change sensing and GNSS signal quality analysis. Note: S1–S9 are fixed monitoring sites with different local environments. The synchronized sites P1, P2, and P3 correspond to S11 and S10: P1 is located near S11, while P2 and P3 are located near S10.