Abstract: Using a lots of wireless sensor node to organize the ubiquitous computing network，how to make net transport securely is key problem of ubiquitous computing research.The paper proposes a new bivariate polynomial key pre-distribution scheme based on three-tier hierarchical network architecture，the new key management scheme is established pairwise key between any two cluster heads and is suitable for the limited battery power，memory storage，data processing capacity condition.The scheme not only successfully improves the network resilience against node capture attacks but also solves the “K-security” problem of polynomial-key pre-distribution schemes.