Based on the data of Lanzhou digital telemetry seismic network（Lanzhou DTSN）, using four parameters（rco, Rco,Sco1, Sco2） from three amplitude ratios among some body waves and first motion of seismic wave, which are amplitude ratio of end portion in the wave, amplitude ratio of P and S waves,and amplitude ratio of first motion of P wave and the maximum amplitude of S wave,the anomolies before Jingtai earthquake（MsS. 9） on June 6,2000, Sunan earthquake （Ms 5.3） on July 11,2001, and Xinghai earthquake （Ms6.6） are analyzed and researched. The result shows that each type of amplitude ratio appears high value better moderate-strong earthquakes in 1-4 months, among them parameter Scol and Sco2 have better relation with earthquake. That means,because the frist motion of P wave arrives station first and is not disturbed by other waves,the amplitude ratio of it cna reflect the information of seismogenic region directly.