In this paper, the creep behavior of the plastic power package at high temperature 155 °C was studied by real time moiré interferometry and FEM modeling. 1200 l/mm grating was replicated onto the cross-section of the specimen at room temperature. The specimen was held at 155°C (around the Tg of the epoxy molding compound) in the vacuum chamber for about 13 hours. The thermal deformation and creep of the specimen was recorded and measured in situ by moiré interferometry. The experimental results show that creep deformation occurs in the epoxy molding compound. The non-linear viscoelastic constitutive model was used for FEM simulation. The simulation results were compared with the experimental results and they were matched quite well on the global deformation of the specimen. The calculation results also show that, accompanied with the global creep deformation in molding compound epoxy, local stress concentration decreased significantly.