[Objective] In order to investigate the amount of virus released from silkworm infected by Bombyx mori bidensovirus (BmBDV) at the different periods and to develop a method for rapid and accurate detection whether silkworm were infected by BmBDV or not. [Methods] A small fragment of ns1 gene of genomic segment VD1 and ns3 gene of VD2 were cloned to pMD18-T vector respectively, and then the standard curve of ns1 and ns3 was obtained. The release dynamics of BmBDV were investigated by detecting the amount of BmBDV in the faeces of 5th instar silkworm at different infection stage. [Results] The results shown that a lot of virus were detected in silkworm faeces at the 3 days post-infected about 1.38×106 copies/μg VD1, 6.54×105 copies/μg VD2. The amount of virus increased exponentially from 5 days post-infected. The amount of BmBDV reached a plateau at 7 to 8 days post-infected about 2.12×107 copies/μg VD1, 1.34×107 copies/μg VD2. The PCR results also indicated a similar dynamics. [Conclusion] The release dynamics of virus suggests that the replication cycle of BmBDV is about 60 h. The infection of BmBDV in silkworm can rapidly, simply and accurately be determined by detecting the virus in silkworm faeces using real-time quantitative PCR.