Extenics is a newly developed interdisciplinary subject combining mathematics, philosophy and engineering. It providesuseful formalized qualitative tools and quantitative tools for solving contradictory problems. In this paper, extension theory isintroduced briefly and the primary applications of this theory and methods in bionic engineering research are discussed. Theextension model of biological coupling functional system is established. In order to identify the primary and secondary sequencingof coupling elements, the Extension Analytic Hierarchy Process (EAHP) was adopted to analyze the contribution ofeach coupling element to the coupling functional system. Thus, the influence weight factor of each coupling element can bedetermined, so as to provide a new approach for solving primary and secondary sequencing problem of coupling elements in aquantitative way, and facilitate the subsequent bionic coupling study.