After a deep search for this, I have reached FlexJS for Cross Compiling Adobe Flex Applications to HTML.
FlexJS requires us to learn new MXML syntax as all the MX or Spark Components are re-written.
As i see migrating from existing SDK 3.5 application will be challenging and will not be smooth as you will end up reworking on your existing code.
So are there any other cross compilers that can compile existing FLEX SDK 3.5 based applications to HTML with out migrating the code?