FL teacher's peer mentoring has been considered an effective professional development practice and widely practiced among western countries， which offers new insights for FL teachers' professional development in our country． However， research on peer mentoring evaluation is scarce． Based on the intrinsic values of peer mentoring， which are “equally communication” ， “negotiation and reflection” ， “mutual benefits” ， the paper discusses the main principles， criteria and methods of evaluation， therefore establishing an initial evaluation system for FL teacher peer mentoring．