The Spodoplera litura Nuclear Polyhedrosis Viruses （SINPV）is a kind of insectile virus with a simple structure

in which a double helix DNA is encapsulated in a protein coat and there is no function of enzymatic repair. In this study

the SINPV samples in dry powdered form held in sealed plastic tube were irradiated by 1-100kGy gamma rays. The single strand breaks （SSB） and double strand breaks （DSB） induced in SINPV after irradiation were measured by neutral and alkaline agarose gel eletrophoresis.A dose-response function combining the responses of one-hit and two-hit events was used to describe the SSB and DSB dose-response curves. It is shown that the SSB are one-hit events and the DSB are the combination of both one-hit

and two-hit events

and two-hit events are predominant in the DSB process.