Abstract: This study focuses on the data validation challenges of eight types of payloads in four major categories (electromagnetic field, in-situ plasma, energetic particles, and ionospheric structure) carried by China Seismo-Electromagnetic Satellite (CSES), the in-orbit full-chain validation system for electromagnetism satellite data in China has been established. This system vertically achieves precise end-to-end validation from "raw electrical signals to physical quantities and then to data products" for each payload. Horizontally, it conducts multidimensional cross-validation among payloads, satellites, and ground-based observations, as well as between models and measurements, utilizing natural phenomena such as magnetic storms, lightning, and strong earthquakes, along with artificial signals like very low-frequency (VLF) transmitters. As a result, the validated data from CSES have reached an internationally advanced level overall, with some indicators leading globally. The magnetic measurement data have been recognized by the European Space Agency's Swarm team and incorporated into mainstream international models as a key data source. Key achievements include: achieving high-precision in-orbit validation and interference suppression for vector magnetic fields, with data accuracy improved to better than 1 nT; proposing electromagnetic field time synchronization correction tool, achieving synchronization accuracy better than 0.1 seconds; revealing the impact mechanisms of satellite platform material degradation and illumination conditions on plasma observations, and proposing dynamic bias adjustment solutions; quantitatively assessing proton contamination in high-energy particle observations using solar proton events; and optimizing ionospheric TEC inversion and correction methods to obtain high-precision electron density profiles. This system has been applied to the data product generation of CSES-01 and has driven the implementation of nine key improvements in the CSES-02 project, significantly enhancing satellite observational performance. The calibrated data products have served fields such as earthquake monitoring, space weather, national defense security, and scientific research, earning recognition from international peers and laying a key technological foundation for China's transition from "catching up" to "keeping pace" and even "leading" in related technological domains.