Gynaephora qinghaiensis is an important pest that damages alpine meadow vegetation in Qinghai-Tibet Plateau (QTP) alpine pastoral areas. Pteromalus sanjiangyuanicus Yang is a parasitic natural enemy of pupal G. qinghaiensis. For biological control of G. qinghaiensis, local materials and G. qinghaiensis were used for P. sanjiangyuanicus propagation. Under natural field conditions, P. sanjiangyuanicus were propagated in artificial nests. Propagated P. sanjiangyuanicus were then released into the experimental area, where the G. qinghaiensis density was high, and the biological control effect was evaluated. In the propagation test plot (D), the average P. sanjiangyuanicus parasitism rate was 70.3% (46.3–87.0%). The P. sanjiangyuanicus parasitism rate in the experimental area was significantly higher than that in the control area, and the propagation effect was good. The P. sanjiangyuanicus parasitism rates in the biological control plots (A, B, and C) increased yearly from 2016 to 2019, indicating that the P. sanjiangyuanicus population size in the biological control area increased yearly and that the parasitoid population size effectively increased. From 2016 to 2019, the G. qinghaiensis population decline rates in the biological control plots (A, B and C) were 71.1%, 59.3% and 76.4%, respectively (average 68.9%). The control effects on G. qinghaiensis were 80.9%, 69.9% and 80.3%, respectively (average 77.0%). The results showed that P. sanjiangyuanicus was effective in controlling G. qinghaiensis. This study provides a reference for the large-scale propagation of P. sanjiangyuanicus and the further promotion and application of G. qinghaiensis biological control.