The dynamic changing feature of Semantic Web determines that the ontology which is a part of Semantic Web needs constantly to be modified in order to adapt outer environment. In this paper we make a careful analysis of the ontology changes' complexity under open environment. The main contents discussed are as follow. At first we point out all possible relation types between any two ontology change sequences including directly conflict relation, indirectly conflict relation, dependent relation and compatible relation according to ontology change's definition. And then we propose a new algorithm named Algorithm of Searching Maximum and Sequential Ontology Change Sequence Set(ASMSOCSS) to find all maximum and sequential ontology change sequence subset in the prime ontology change sequence set and prove the independence of the result which may be got after running ASMSOCSS. At last we put forward the algorithm by using these maximum and sequential ontology change sequence sets to create new ontology versions according to the dependence relation between ontology change sequences.