Abstract: The process of contamination between batches is a process of two-dimension convection-diffusion.The bigger numerical dispersion and non-physics surge phenomena are existed in commonly used numerical methods.The double-time splitting method,which is a solving method of diffusion equation that mainly be controlled by convection,is proposed by the combination of characteristics method and finite difference method.The method,which is faster,small storage and unconditioned stabilization,is applied to solve the convection-diffusion equation and analyze the contamination in batch transportation of oil products.The results of numerical computation conform to engineering and explain the forming and developing of contamination very well.Thus,it proves that the method is right.