To address the problem of low synchronization trigger accuracy in synchronous acquisition of mechanical vibration in wireless sensor networks, a cross-layer synchronous acquisition trigger method with proportional compensation is proposed. Firstly, the ultra wide band mechanical vibration wireless sensor network nodes based on cross-layer synchronous architecture are designed, and the composition of the actual acquisition clock of the acquisition node is analyzed. Then, a hardware timer is used as the acquisition control clock to obtain the synchronization information across layers and carry out the delay of synchronous trigger. Finally, the time scale model between nodes is formulated according to the periodic synchronization information, and the delay time of synchronous trigger is proportionally compensated according to the uplink time scale of the acquisition node to reduce the synchronous trigger error. Experimental results show that the mean value and maximum value of synchronous acquisition trigger error in single-hop network are 20 and 50 ns, and the mean value and maximum value of synchronous acquisition trigger error in two-hop network are 37 and 76 ns, which effectively improve the synchronous acquisition trigger accuracy of mechanical vibration wireless sensor network.