With the widely application of the Wireless Sensor Network, it is particularly significant to assure a secure communication mechanism between the nodes. In order to meet the needs of sensor nodes on low power consumption and less resource, lightweight cryptographic algorithm designed well is the key to constructing a riskless WSN scheme. In this paper, we propose an improved elliptic curve cryptography digital signature scheme by means of optimizing the multiplicative inverse module of ECDSA, based on ECC lightweight cryptographic algorithm. Moreover, we implement ECDSA scheme improved on Micaz, which is a kind of sensor network platform. And then, experimental results demonstrate that the performance of improved scheme is superior to the previous, not only on the speed but also on the efficiency, under the same experimental environment and encryption intensity. In a word, our scheme has stronger practicability.