Abstract: Codec is a necessary part of TTCN-3test system which transfers TTCN-3template data to SUT input data,and SUT output data to TTCN-3template data．This paper presented the design of generic codec for testing Web application．The generic codec needs to transform TTCN-3template into URL request string,and extract Web page content to transform into TTCN-3template．Conscious of the Web pages with large volume of data and noise data,this paper presented the multi-level parsing and composition strategy．Experiments show that the strategy works well, and could save much codec development effort.

Key words: TTCN-3,Test system,Web application testing,Codec,Multi-level parsing