Cyanophage can proliferate rapidly in the late stages of cyanobacterial blooms. Cyanophage lysis of cyanobacteria has been considered an important pathway that can induce cyanobacterial apoptosis. However, few reports have focused on the use of cyanophages. In this study, the infection of Anabaena sp. PCC 7120 by cyanophage A-4(L) was used as an example to investigate the influence of illumination, temperature and multiplicity of infection on cyanophage lysis, which can help us to determine the best timing and concentration of cyanophage addition. Our results showed that illumination was a key factor affecting cell lysis. A-4(L) lysed Anabaena sp. PCC 7120 after 8 hours at a MOI of 0.01 during continuous illumination, whereas no lysis occurred during dark incubation. In addition, prolonged illumination resulted in more rapid infection. Further studies showed that adsorption was not dependent on illumination. However, intracellular replication of cyanophage DNA was inhibited under dark conditions. It is speculated that the replication of A-4(L) DNA may be related to the photosynthesis of the host. Within the range of 15-25℃, higher temperature improved the lysis rate. The extracellular A-4(L) titer also increased with higher temperature. In the range of 10^-6-1, A-4(L) lysed cells 4 h earlier when the MOI increased by two orders of magnitude. Taken together, we proposed the addition of cyanophage at a MOI of 0.01 between 7:00 and 12:00 for the purpose of bloom treatment. Further field experiments showed that the addition of cyanophage at a MOI of 0.01 at 7:00 am did indeed significantly reduce the biomass of PCC7120 algal cells by 76% within 24 hours. This study provides a basis for using cyanophages to control the abundance of cyanobacteria during cyanobacterial blooms.