Internal charging is generated by penetrative electrons from the outer radiation belt, and the resultant discharges usually occur inside spacecrafts or sdeeply in the surface dielectrics. Therefore it may produce more serious results in electronics on board compared with surface charging. In this article, the general characteristics of internal charging were introduced, and, as an example, an internal charging induced anomaly, which took place on Double Star (TC-1 and TC-2) was analyzed through correlation of the anomaly with high energetic electron enhancement. The analysis provides a typical instance for spacecraft anomaly diagnostics.