Wikipedia as a largest knowledge base is an important platform for sharing knowledge in the world．It can help understand the developing trend in the science，technology and society through the macro-level statistical properties of knowledge and their evolution regularities. The semantic of the article in Wiki can be derived from the labels and the info box in the pages, which can be formally represented by ontology. Two important characters of Wiki ontology are proposed. One is there are n-ary relations in it. The other is the size of this ontology is enlarging. Moreover，we propose the evolution mechanism of the ontology of Wiki. The main contents of the paper are shown as follows. 1) With the data from YAGO, the method of constructing hypernetwork of Wiki ontology is proposed. 2) After the analyzing the basic topological quantities of the hypernetwork，we propose an evolving mechanisms of the hyperedge growth. 3) The results of analyzing and numerical simulations are given at last．