An insertion module adapted to guide an insertion needle to move stably before inserting into a host, characterized by: a main body having an accommodating hole extending along an axial line, and a plurality of slide grooves disposed on said accommodating hole around the axial line and communicating with said accommodating hole; an auxiliary insertion seat having a base portion, and a plurality of wing portions connected to said base portion, wherein each of said wing portions is reciprocated within a respective one of said slide grooves, and has a protruding portion; an insertion needle assembly including a needle seat assembled with said base portion of said auxiliary insertion seat, and an insertion needle connected to said needle seat, wherein a distance between a tip end of said insertion needle and a skin surface of the host is defined as an initial stroke distance; and a sensor assembly including a sensing seat, and a sensor held within said sensing seat, wherein said sensing seat is assembled with said base portion of said auxiliary insertion seat, and said insertion needle is inserted through said sensing seat to cover said sensor; wherein each of said slide grooves has a wall surface, and said protruding portion of each of said wing portions resiliently abuts against said wall surface of a respective one of said slide grooves in point-contact such that said auxiliary insertion seat is fixed before inserting into the host through the interference between said protruding portions and said wall surfaces to provide a stable inserting and prevent said insertion needle from oblique in said initial stroke distance; and characterized in that said wall surface of each of said slide grooves is gradually widened along an insertion direction. a main body having an accommodating hole extending along an axial line, and a plurality of slide grooves disposed on said accommodating hole around the axial line and communicating with said accommodating hole; an auxiliary insertion seat having a base portion, and a plurality of wing portions connected to said base portion, wherein each of said wing portions is reciprocated within a respective one of said slide grooves, and has a protruding portion; an insertion needle assembly including a needle seat assembled with said base portion of said auxiliary insertion seat, and an insertion needle connected to said needle seat, wherein a distance between a tip end of said insertion needle and a skin surface of the host is defined as an initial stroke distance; and a sensor assembly including a sensing seat, and a sensor held within said sensing seat, wherein said sensing seat is assembled with said base portion of said auxiliary insertion seat, and said insertion needle is inserted through said sensing seat to cover said sensor; wherein each of said slide grooves has a wall surface, and said protruding portion of each of said wing portions resiliently abuts against said wall surface of a respective one of said slide grooves in point-contact such that said auxiliary insertion seat is fixed before inserting into the host through the interference between said protruding portions and said wall surfaces to provide a stable inserting and prevent said insertion needle from oblique in said initial stroke distance; and characterized in that said wall surface of each of said slide grooves is gradually widened along an insertion direction.