The invention provides a topology discovery method and system for massive wireless sensor networks. The method comprises the steps that in the wireless sensor networks, a plurality of wireless sensor nodes declare to be cluster heads, and cluster head declaration is broadcasted; the wireless sensor nodes not joining in clusters join in the clusters and forward the cluster head declaration after receiving the cluster head declaration; the wireless sensor nodes joining in clusters adjust links of the wireless sensor nodes; the wireless sensor nodes of a current cluster declare themselves to be gateway nodes of the current cluster and other clusters when receiving first cluster head declaration of other clusters; the other wireless sensor nodes of the current cluster adjust the gateway nodes; the hop count is adjusted according to energy levels of the nodes; and a topology discovery process of the massive wireless sensor networks is restarted every other fixed time interval. According to the topology discovery method and system for the massive wireless sensor networks, the data transmission links of the wireless sensor networks can be established rapidly, the network average energy consumption is reduced; and the network lifetime is improved.