Historically,there have been many restorations and explorations of the structure of the Houfeng seismograph,but there are unreasonable points. This has caused the public and some scholars to question its authenticity,so a reasonable principle model needs to be proposed. We found a stable inverted pendulum structure that does not require the use of springs. It have a low natural frequency while ensuring the size and manufacturing process in line with historical facts,and can be used to develop the Houfeng seismograph that meets the requirements of the later Han. And we simulated the structure in matlab. The result proves that the structure can respond to the seismic wave and issue a warning. It is a reasonable model of the Houfeng seismograph.