A method for generating a Simple Object Access Protocol (SOAP) message in XML during execution of a process in a SOA-based process engine apparatus and a corresponding process engine apparatus. The method includes: generating and storing an XML character string containing a fixed SOAP message skeleton; generating and storing an XML character string containing an instance-constant variable; generating an XML character string containing a dynamic variable; and concatenating the XML character string containing the fixed SOAP message skeleton and the XML character string containing the instance-constant variable as previously stored and the XML character string containing the dynamic variable by a character string concatenating operation to generate a SOAP message. A process engine apparatus including a message analyzer unit, a message pre-composer unit, a character string depository, and a message composer unit is also provided.