Abstract: According to in-situ investigation, theoretic analysis and model testing research, the factors affecting the scouring span of subsea pipeline in Cbengdao Oilfield are analyzed in this paper. The control methods for unsupported scouring span of subsea pipeline, such as "grout bags hackfilling with concrete mattresses covering", "under water piles supporting" and "flexible pipe jumping", are discussed. The advantages and disadvantages of these methods are compared and some suggestions for design, installation and operations of subsea pipeline in Chengdao Oilfield are also given in this paper.