Abstract: Drilling riser is the important equipment from subbottom wellhead to drillship. As offshore drilling activities expand to more deeper water areas, the force acting to the marine riser becomes more and more complicated. As the water depth increases, the characteristic analysis of the marine riser becomes more and more important. The paper uses four-order differential equation, and a mechanical analysis is numerically simulated by using a finite-difference method. The effect of top tension and buoyancy blocks on the offshore riser is studied, and the corresponding software was drawn up. It is shown that the mechanical analysis method and computing program in this paper are simple，accurate and fast computation. It provides a reliable theoretical basis and guidance for the design and check of the marine riser system, and possesses of high application value.