Abstract: Whispering-gallery-mode disk microcavity,as a new photonic sensor,is a useful component for detecting biological pathogens.It’s significant to understand the light propagation in WGM disk microcavity coupled to submicron-width waveguide.It is investigated a two-dimensional WGM disk microcavity by solving Maxwell equations with the finite-difference time-domain method (2D-FDTD).The 2D computation reveals that the existence of absorbing particles will change the light propagation.This calculation is helpful to the design of optimized high-sensitivity photonic biosensors.