Lasing mode regulation is essential for realizing the practical applications such as optical communication and optical sensing/switches. In this work, we etched the slit along the c-axis of a hexagonal ZnO microrod by focusing ion beam etching. This slit can produce very strong local light field under strong incident light. Compared with the bare ZnO sample, whispering gallery mode (WGM) lasing mode is reduced, while the emission intensity decreases and the laser threshold increases. Then Ag nanoparticles filled the slit as nonlinear absorbers. the regulation of WGM laser mode is realized by the coupling effect of non-linear absorption effect of Ag nano-particles and the local light field. Moreover, laser mode intensity is enhanced by strong coupling between ZnO microrod and surface plasmon resonant of Ag NPs of its surface that is proved by PL decay time.