Abstract: The in-orbit satellites’ failures caused by space radiation environment are analyzed by statistics. The phenomena and the mechanism of a typical in-orbit SEU failure of an integrated data processor are discussed in detail, with consideration of countermeasures. Based on the analyses of some real cases of in-orbit failures, the engineering experiences and the simulation analyses, this paper proposes methods for radiation hardening through hardware and software approaches, which may help mitigate the SEUs and extend the service life of satellites.