In this paper, a new measure of wireless sensor network connectivity is proposed based on the charac- teristics of the data collecting network. A new definition of invulnerability is proposed, and two measures of invulnerability are proposed for the two different damages. At last, this paper studies the invulnerability of the wireless sensor networks based on the small-world model. The simulation indicates that it is a new and effective method to research the invulnerability for the wireless sensor networks.