Abstract: The vapor bubble nucleation effects on heat-transfer and fluid flows in microchannel are investigated based on an improved hybrid lattice Boltzmann model. The dynamic process of bubble growth, departure and motion are simulated in microchannel with different physical conditions, while the process influences on fluid flow and heat transfer are also quantitatively predicted respectively. The results show that the bubble nucleation on reentrant cavity can induce the periodic flow instability; through it also strengthens the efficiency in heat transfer around the bubble.