Aiming at the problem of choosing the tide level range of loading and unloading operation on ro-ro wharf,we take the straight type ramp as a research object,and analyze the influence on loading and unloading tide level of factors including ramp technical parameters,ship condition,vehicle traveling capacity and wharf parameters,and quantitatively convert the influence to a system of inequalities with ramp working angle as the only unknow,solve the system of inequalities by a numerical iteratively method,forecast the suitable tide level range,and verify the forecasting process by an engineering example.The results show that the method is applicable to the prediction of tide level,and it can be used to guide ro-ro ship to make the loading and unloading plan.