Abstract: Taken cylindrical monopile as the research model,the local scour of monopile under unidirectional and tidal current was investigated through local scour flume tests. The effect of anti-scour collar on the local scour of monopile was studied as well. The experimental results of this study shown that the maximum scour depth under tidal current is 60%-80% of that under unidirectional current,the anti-scour collar can reduce the local scour depth of the monopile under both unidirectional and tidal current,and the protection effect of anti-scour collar can be enhanced by either decreasing the installation height or increasing the outer diameter.