Effects of surface roughness and fouling on ship resistance are analyzed by numerical simulation, the fouling covered on hull are graded through the visual inspection, three different hull surface conditions are divided corresponding to three models used to simulate by FLUENT software through computational fluid dynamics (CFD) method. The simulation results are compared with the empirical conclusions, and the resistance growth and resistance properties are analyzed. It shows that poor hull surface conditions make ship resistance increase, added resistance increase with speed grow under the same surface condition. On the condition of surface roughness (including mild fouling) and moderate fouling, the increased resistance is mainly frictional resistance, however, there is not the same under the condition of heavy fouling that viscous pressure resistance, wave resistance increase more than frictional resistance, and the recommended coefficient is not applicable to the reality situation under the condition of heavy fouling, the results calculated though CFD method are useful. Speed reduce is helpful to drag reduce on any surface condition of ship.