Hybrid colloidal capsules have been increasingly applied in various areas involving high-temperature conditions due to their superior thermal and mechanical stabilities compared to traditional colloidal capsules. However, the mechanics of the hybrid microcapsule in response to temperature and the chemistry underpinning it have not been well investigated. Herein, we have revealed the significant modifications in the mechanical properties of the calcium carbonate (CaCO3)-decorated silica (SiO2) double-shell hybrid microcapsule at different annealing temperatures. The underlying mechanism of such changes has been elucidated by directly visualizing the high-temperature interfacial solid-state reactions in the hybrid double shell. In particular, time-of-flight secondary ion mass spectrometry (TOF-SIMS) coupled with microelectromechanical system (MEMS)-based microheater has been first utilized to image the chemical diffusion during the solid-state reactions. Such chemical diffusion results in the phase evolution and the structural transformation of the hybrid double shell, which have been demonstrated by in situ heating X-ray diffraction (XRD) and in situ heating transmission electron microscope (TEM), respectively. The results obtained in this study have broadened the fundamental understanding of the mechanics of the hybrid microcapsule at high temperatures, which will advance the fabrication of enhanced and novel hybrid microcapsule systems for harsh operating conditions.