Abstract: The problem that the life of drilling equipment is long or short is not only concerned with the natural life of drilling equipment but also concerned with their technical and economic life.The natural life of drilling equipment forms the basis of their renewing.Besides,the technical and economic life of drilling equipment is the key to their reforming and renewing.The author recommends that the best plan for reforming and renewing drilling equipment is to let the total costs of drilling equipment investment and annual support fee reach minimum value.And the best renewal time of drilling equipment can be determined by the way of calculating.