Abstract: Disclosed is a pH-sensitive hyaluronic acid derivative, comprising at least one repeat unit as shown in the following formula (I), wherein HA represents a unit comprising N-acetyl-D-glucosamine and D-glucuronic acid, q represents an integer of 2 to 10,000; A represents a biocleavable linkage comprising at least one of hydrazone, acetal, ketal and imine; M represents at least one of a hydrophobic fragment, a hydrophilic fragment, and an amphiphilic fragment, and p represents the number of [A-M] directly grafted onto each HA unit, p represents an integer of 0 to 4, and the p of each HA unit is not 0 at the same time.