Disclosed is a nanobody against the human programmed death factor PD-LI. The antibody has the function of blocking the binding of PD-LI to the receptor PD-I. Disclosed are the nanobody and the gene sequence encoding the nanobody, the corresponding expression vector and the host cell capable of expressing the nanobody, and the method for producing the nanobody. At the same time, also disclosed is the sequence of the humanized PD-LI nanobody. The humanized nanobody still has the function of blocking the binding of PD-LI to PD-1, and has a relatively high affinity and a relatively good specificity.