Abstract: An method of instruction retrieve is proposed for microcontroller, which can takes the advantage of the relationship between instructions executed in microcontroller and the side channel leakages such as power consumption and electromagnetic emissions, builds side channel templates for instructions and matches the side channel trace from an unknown instruction to retrieve the operation. However, there are usually so many points in a side channel trace that the compute efficiency is very low. An interest component selection method with principle components analysis (PCA) is proposed to select interest components from side channel trace. With about 30 components selected from about 400 sample points, the correct matching ratio gained by PCA is about 50% higher than that by selecting points artificially.