Microsoft Dynamics AX report web parts are used in Role Centers and in Enterprise Portal pages. If you need to pass parameters to the report throug query string , you can do so  in the URL with this syntax  <selector>.Parameters.<parameterName>=<parameterValue>

For example In the Ax report webpart , set the parameter selector value to Report1. And let us say the report has a parameter defined with the name CashInflowvsCashOutflow_EndDate. In that case the query string will be

http://axepdemo/sites/DynamicsAx/Enterprise%20Portal/RoleCenterCEO.aspx?WCMP=CEU&Report1.Parameters.CashInflowvsCashOutflow_EndDate=10/01/2007