Having the ability of handling complex transaction in heterogeneous environment, workflow is coming into notice in the area of science research, e-government, e-business, there are lots of research achievements and productions. Major parts of the studies are concentrated in the workflow scheduling, interface with database and legacy system, etc., few efforts are put into the researches of architecture, model and definition language of workflow management system. In this paper, workflow meta-model of WfMC is analyzed. According to real cases, extensions and modifications to workflow meta-model and workflow definition language are introduced, so as to satisfy the increasing variability of business process and application of new technologies.