Fatigue test is carried out for 16MnR steel weldment. The compact tension (CT) samples with 3.8mm thickness are used, and comparisons of fatigue crack growth between base metal and fusion zone in the weldment are considered in Paris region. It is shown that fatigue crack growth rate in the base metal is not sensitive to R-ratio, but the crack growth rate in the fusion zone increases with R-ratio increasing. To the low R-ratio, the crack growth rate in the fusion zone is smaller than that in the base metal, but they approximate the same under the high R-ratio. The mechanism of fatigue crack growth is analyzed through crack growth path in the microstructure, the different of fatigue crack growth behavior is studied for the base metal and the fusion zone.