Intermediate bearing is an important part of aero-engine supporting transmission system, and its running state directly affects the working state and operation safety of aero-engine. On the basis of vibration signal analysis and processing, aero-engine intermediate bearing weak fault feature signal extraction experiment was carried out. An analog casing was designed and processed to simulate the complex transmission path of vibration signal. Based on envelope spectrum analysis and empirical mode decomposition (Empirical Mode Decomposition) envelope spectrum analysis, the vibration signal was processed, and the extraction effect of the weak fault characteristic signal of rolling bearing was compared. Experimental results show that in the extraction of weak fault characteristic signal of intermediate bearing, the analog casing can effectively simulate the complex transmission path of vibration signal, the EMD envelope spectrum analysis method can extract the weak fault signal of intermediate bearing more obviously and effectively than the single method using envelope spectrum analysis.