Abstract: A Ms4.2 earthquake occurred in Qian'an city on May 12,1999.Before the quake the quiet period of earthquake has been lasted 8 years in the old area of Tangshan earthquake.The seismic energy showed a low value anomaly of 5 months.The underground water level of Xifabao well in Luanxian county showed an accelerating rising anomaly against its yearly variation.According to these anomalies Seismological Bureau of Tangshan City gave this earthquake a successful imminent prediction.