Due　to　the　geometric　distortion　in　distorted　hydraulic　laboratory　experiments,　velocity　profile　cannot　maintain　as　constant　as　required　by　the　traditional　criteria.　Scaling　effects,　which　lack　quantitative　researches,　cannot　be　avoided　even　if　the　Froude　and　drag　coefficient　similitude　criteria　were　satisfied.　Prediction　formulas　of　scaling　effect　rate　are　established　in　this　research　to　theoretically　reveal　the　quantitative　relations　between　velocity　profile　distortion　and　experimental　parameters.　They　are　directly　related　to　three　parameters,　distorted　ratio,　relative　water　depth,　and　relative　bed　roughness.　In　vertical　direction,　most　effects　happen　near　the　bed　and　the　deviation　increases　with　distortion　ratio.　The　similarity　of　secondary　flow　is　worse　and　more　complicated　than　that　of　stream-wise　flow.　The　correction　method,　which　is　the　improvement　of　traditional　similitude　criteria,　can　effectively　reduce　scaling　effects　when　converting　experimental　results　into　their　corresponding　values　in　the　prototype.　Three　dimensional　numerical　models　are　built　to　verify　the　accuracy　of　the　prediction　formulas　and　correction　method.　©　2019　The　Author(s).　Published　by　Desalination　Publications.