Abstract: For the advantages of security and computation, elliptic curve cryptography is widely used in smart cards. Width-w NAF method with small space and high speed, is favored by elliptic curve cryptography. The present of power analysis attacks give us a new way to examine the security of smart-card. This paper presents an improved algorithm based on width-w NAF method to resistant power analysis attacks, including simple power analysis attacks, differential power analysis attacks, refined power analysis attacks and zero-value point attacks, without increase any computation of main loop.