Abstract: In order to optimize the immunization procedure of avian influenza in commercial layer farms,master the growth and decline rule of maternal antibody against H5 subtype avian influenza in commercial layer farms and the antibody titer of trivalent inactivated vaccine（Re-6 strain+Re-7 strain+Re-8 strain）against H5 subtype avian influenza virus at different first immunization days.The commercial layers were divided into5 groups in this experiment.Groups 1-4 were immunized with trivalent inactivated vaccine of H5 subtype of avian influenza virus at 7,10,14 and 21 days of age,respectively.Group 5 was the blank control group,and the normal saline was injected intramuscularly at 14 days of age,and then avian influenza antibody was detected.The results showed that the maternal antibody level of laying hens was the highest at the age of 2 days,the average titer was more than 6 log2,and the qualified rate of group antibody was more than 99%.Then,it decreased gradually,and it was near 6 log2 at the age of 10 days,which indicated that the chickens were at high risk of avian influenza virus infection;when the first immunization age was 7 days and 10 days,the protective antibody produced by the vaccinated chickens was about 14-17 d,and the maternal antibody level was also low.The antibody produced by the vaccinated chickens was not enough to protect chickens.If the first immunization age is after 14 days,it will be more unfavorable for the prevention and control of avian influenza in chickens.We suggested that the first immunization time of H5 subtype avian influenza vaccine should be 7 days old.