Abstract: In order to measure the availability of heterogeneous wireless sensor networks (HWSNs), a new Susceptible Exposed Quarantined Infected Recovered Dead (SEQIRD) model with heterogeneous sensor node states is proposed, which is more suitable for the actual situation. The semi-Markov process was utilized to depict states of the node's dynamic transition process, and the steady-state probability of each state was obtained. The entire HWSNs steady-state availability under different topologies could be computed. Numerical analyses were performed to verify the influence of the initial infection rate, infection change rate and recovery rate on the steady-state availability of HWSNs.