On December 14,2002, A destructive M_S5.9 earthquake occurred at Yumen city, Gansu province, and it caused damage to building structures and other engineerings. After the earthquake, the investigation of seismic field and the assessment of seismic disaster are done. On the base of general situation, natural environment, social economy, main industry, population and building situation in seismic area, the seismic area is divided into 7 parts, and the 66 investigating samples points are finished. According to the loss assessment system of seismic disaster(EDLES), a databank is set up, and a relatively practical assessment of economic loss is done.