A method for managing a host memory buffer, a memory storage apparatus, and a memory control circuit unit are provided. The method includes: detecting whether a system abnormality occurs; copying a first command and first data corresponding to the first command stored in a data buffer of a host system to the memory storage apparatus in response to determining that the system abnormality occurs; executing an initial operation after copying the first command and the first data, wherein the initial operation initializes a part of a hardware circuit in the memory storage apparatus and does not initialize another part of the hardware circuit in the memory storage apparatus; and re-executing the first command stored in the memory storage apparatus after initializing the part of the hardware circuit.