Abstract: Owing to the fact that sampling ways and propagation paths of vibration signals under embedded ways are much different from those of traditional methods,the fault vibration propagation characteristics in a gearbox under the condition of embedded sensing were studied based on finite element simulations.Then,an optimal placement model was built based on signed directed graph(SDG) of faults vibration propagation in a gearbox,and a solution algorithm was proposed based on particle swarm optimization(PSO).Finally,an example was presented and simulation results demonstrate that the proposed methods are feasible,providing an effective way to embed sensors into a gearbox.