Objective    To reveal the characteristics and revolutions of PB1 gene of human avian influenza H

5

N

1

subtype by analyzing its mutation.    Methods    The PB1 gene of H

5

N

1

viruses isolated in Guangdong was sequenced

and the global PB1 genes of the viruses were obtained from internet；They were analyzed by DNAStar Lasergene by me

ans of studying the revolutionary speeds with the epidemiological data.     Results    PB1 genes of 50 strains during 1997 to 2006 were homologouslly classified into 2 groups

the strains from Hong Kong during 1997 to 1998 (G1) and the strains during 2003 to 2006 (G2).Totally 74 amino acids were substituted in PB1 gene in all strains，with ratio of 9.78%（74/757）. In the synonymous variation，Ks values in PB1 were 26.1×10

-6

to 39.8×10

-6

Nt/d and Ka values in PB1 were 3.91×10

-6

to 5.59×10

-6

Nt/d，where there existed obviously the automatic substitution and obviously negative selective pressure by biological test.G2 strain were found with a deletion of a glycine (757)

and G1 strains had a lose of glycosylation site of NES

382-384

.     Conclusion    PB1 genes were classified into 2 groups and evolved rapidly by spontaneous substitution，which is similar to PB2 genes in gene evolution between time feature and district feature. Deletions of G

757

and NES

382-384

in strains during 2003 to 2006 are worth further researching about clinical significance in the future.