This study, based on a large-scale nationwide questionnaire survey, investigated English teachers’ perceptions on the washback effects of the NMET on senior high school English teaching and learning. Both descriptive and inferential statistical analyses were implemented to analyze the quantitative data collected by the questionnaire, and the qualitative data were analyzed on the basis of the Grounded Theory. The findings showed that a large majority of English teachers thought highly of NMET washback on senior high school English teaching and learning. Despite the pressure and challenges it had brought to teachers and students due to its high stakes, the NMET was playing positive roles in promoting students’ English learning motivation and interest, improving their comprehensive English ability and laying foundation for their future study. The NMET was also found to have directly influenced the designs of teaching aims, plans and classroom activities in senior high schools. The probit regression analyses revealed that teachers’ length of teaching and the entry requirements of their school were the two most important factors that had significantly influenced their perceptions on relevant issues.