A monitoring method for a cracking state of a blade, the blade having a root portion and a tip portion in a length direction of the blade, the blade comprising a plurality of blade components and a connecting body, the plurality of blade components being connected with each other by the connecting body and forming a cavity, the plurality of blade components comprising a windward-side shell, a leeward-side shell, and a web plate, the connecting body being connected at least one of: between the windward-side shell and the leeward-side shell, between the windward-side shell and the web plate, and between the leeward-side shell and the web plate, wherein the monitoring methods comprises: a step of providing a pressure transmission assembly, wherein the pressure transmission assembly comprises a side wall, a hollow space enclosed by the side wall, and an opening provided on the side wall and in communication with the hollow space, wherein the pressure transmission assembly is placed within the cavity at a connection between the blade component and the connection; a step of forming a sealed cavity, comprising placing the pressure transmission assembly within the cavity at a connection between the blade component and the connecting body, and fixing the pressure transmission assembly by the connecting body, such that a region around the opening of the pressure transmission assembly and the corresponding blade component are sealingly connected with each other, and the pressure transmission assembly and the blade component together form the sealed cavity with a preset air pressure value, wherein the connecting body is formed by solidification of an adhesive, the pressure transmission assembly extends from the root portion of the blade to the tip portion of the blade; a step of detecting an actual air pressure value, comprising detecting the actual air pressure value within the sealed cavity by using a detector; a step of determining the cracking state, comprising determining the cracking state of the blade according to the actual air pressure value and the preset air pressure value. a step of providing a pressure transmission assembly, wherein the pressure transmission assembly comprises a side wall, a hollow space enclosed by the side wall, and an opening provided on the side wall and in communication with the hollow space, wherein the pressure transmission assembly is placed within the cavity at a connection between the blade component and the connection; a step of forming a sealed cavity, comprising placing the pressure transmission assembly within the cavity at a connection between the blade component and the connecting body, and fixing the pressure transmission assembly by the connecting body, such that a region around the opening of the pressure transmission assembly and the corresponding blade component are sealingly connected with each other, and the pressure transmission assembly and the blade component together form the sealed cavity with a preset air pressure value, wherein the connecting body is formed by solidification of an adhesive, the pressure transmission assembly extends from the root portion of the blade to the tip portion of the blade; a step of detecting an actual air pressure value, comprising detecting the actual air pressure value within the sealed cavity by using a detector; a step of determining the cracking state, comprising determining the cracking state of the blade according to the actual air pressure value and the preset air pressure value.