The measurement performance of seismometer is affected by the natural frequency of beam reed which is the sensitive element of short period seismometer. In order to design the beam reed of seismometer, the finite element model was established used the ANSYS and SOLIDWORKS. From the simulation data, the relationship between vibration pickup reed cross-sectional area and its natural frequency were analyzed. The sensitive element designed by the model obtains the center frequency of 6.1974Hz. Comparing the theory model and the need of design, the error is 3.29%, can meet the requirements of short period seismometer performance requirements.