A grass trimming head, comprising: a housing assembly, formed with a housing cavity and provided with an outer aperture for allowing a cutting line to be inserted from an outside of the housing assembly into the housing cavity; and a spool, at least a portion of which is arranged inside the housing cavity and which is rotatable with respect to the housing assembly about a central axis; wherein the spool is provided with an inner aperture for allowing the cutting line to be inserted into the spool or a clamping portion configured to fix the cutting line, characterized in that: the spool comprises an upper spool portion and a lower spool portion; wherein the upper spool portion comprises: an upper winding portion, configured for winding the cutting line; a first flange portion, connected to an upper end of the upper winding portion; and a second flange portion, connected to a lower end of the upper winding portion; the lower spool portion comprises: a lower winding portion, configured for winding the cutting line; a third flange portion, connected to an upper end of the lower winding portion; and a fourth flange portion, connected to a lower end of the lower winding portion; wherein the upper spool portion is coupled to the lower spool portion to form a line guide passage configured for the cutting line passing through the spool. a housing assembly, formed with a housing cavity and provided with an outer aperture for allowing a cutting line to be inserted from an outside of the housing assembly into the housing cavity; and a spool, at least a portion of which is arranged inside the housing cavity and which is rotatable with respect to the housing assembly about a central axis; wherein the spool is provided with an inner aperture for allowing the cutting line to be inserted into the spool or a clamping portion configured to fix the cutting line, characterized in that: the spool comprises an upper spool portion and a lower spool portion; wherein the upper spool portion comprises: an upper winding portion, configured for winding the cutting line; a first flange portion, connected to an upper end of the upper winding portion; and a second flange portion, connected to a lower end of the upper winding portion; the lower spool portion comprises: a lower winding portion, configured for winding the cutting line; a third flange portion, connected to an upper end of the lower winding portion; and a fourth flange portion, connected to a lower end of the lower winding portion; wherein the upper spool portion is coupled to the lower spool portion to form a line guide passage configured for the cutting line passing through the spool. the spool comprises an upper spool portion and a lower spool portion; wherein the upper spool portion comprises: an upper winding portion, configured for winding the cutting line; a first flange portion, connected to an upper end of the upper winding portion; and a second flange portion, connected to a lower end of the upper winding portion; the lower spool portion comprises: a lower winding portion, configured for winding the cutting line; a third flange portion, connected to an upper end of the lower winding portion; and a fourth flange portion, connected to a lower end of the lower winding portion; wherein the upper spool portion is coupled to the lower spool portion to form a line guide passage configured for the cutting line passing through the spool. an upper winding portion, configured for winding the cutting line; a first flange portion, connected to an upper end of the upper winding portion; and a second flange portion, connected to a lower end of the upper winding portion; the lower spool portion comprises: a lower winding portion, configured for winding the cutting line; a third flange portion, connected to an upper end of the lower winding portion; and a fourth flange portion, connected to a lower end of the lower winding portion; wherein the upper spool portion is coupled to the lower spool portion to form a line guide passage configured for the cutting line passing through the spool. a lower winding portion, configured for winding the cutting line; a third flange portion, connected to an upper end of the lower winding portion; and a fourth flange portion, connected to a lower end of the lower winding portion; wherein the upper spool portion is coupled to the lower spool portion to form a line guide passage configured for the cutting line passing through the spool.