Stiffened plate is a commonly used structure of the spacecraft, in order to develop the onboard monitoring system based on acoustic emission technology, the character of wave propagation in stiffened plate need to be investigated. In the paper, different direction wave speeds in stiffened plate were measured by lead break tests. The effect due to different dimensions of stiffeners had been studied by numerical simulation. Experiment and simulation results showed that the stiffeners had little effect on the extensional wave speed, but it caused the attenuation of the signal amplitude. Consider the signal propagation velocity as a constant, source location...