Abstract: In the paper considering the influence of node's inertia and a constant external field, we establish an public opinion evolution model in which public opinion evolution and network topological structure interact with each othe. It is found that degree distribution gradually gets away from typical power law distribution to Poisson distribution with time evolution under the infuence of node's inertia and a constant external field. With the time evolution in system, there is obvious convergence effect of the public opinions distribution, which not only relates with node's inertia but also depends on the constant external field. It can be obtained that adjusting the value of node's inertia factor and constant external field can control the opinion value's number, which even controls the rate of change.