A method for integrally weaving a shoe embryo having an extension by a flat knitting machine including a front needle bed and a back needle bed, comprising steps of: S10: interweaving an initial shoe edge by knitting at least two yarns (20 and 21) on the front needle bed and the back needle bed; S11: weaving a first shoe upper connected to the initial shoe edge by knitting the at least two yarns (20 and 21) on the front needle bed along a first direction, continuing weaving in a reverse direction when a shoe upper stitch count is reached to weave a second shoe upper facing the first shoe upper by knitting the two yarns (20 and 21) on the back needle bed along a second direction opposite to the first direction, weaving the first shoe upper in a reverse direction according to the shoe upper stitch count, and cyclically performing the above process to weave the first shoe upper along the first direction and the second shoe upper along the second direction; S12: weaving an extension (160 or 161) by knitting at least one of the yarns (20 and 21) when the shoe upper stitch count is reached in the previous step, continuing weaving in a reverse direction when an extension stitch count is reached while the extension (160 or 161) is woven, weaving the first shoe upper and the second shoe upper by knitting the at least two yarns (20 and 21) according to the shoe upper stitch count when the extension stitch count is again reached, and cyclically performing the above process to weave the extension (160 or 161), the first shoe upper and the second shoe upper, so that the extension (160 or 161) extends from where the first shoe upper and the second shoe upper are connected; and S13: cyclically weaving the first shoe upper and the second shoe upper by knitting the at least two yarns (20 and 21), and forming a shoe opening to complete the shoe embryo, wherein the extension (160 or 161) is one of a vamp decoration piece and an ankle strap of the shoe embryo, the extension is connected to a vamp section of the shoe embryo when being the vamp decoration piece, and the extension is connected to a heel section having the shoe opening of the shoe embryo when being the ankle strap. S10: interweaving an initial shoe edge by knitting at least two yarns (20 and 21) on the front needle bed and the back needle bed; S11: weaving a first shoe upper connected to the initial shoe edge by knitting the at least two yarns (20 and 21) on the front needle bed along a first direction, continuing weaving in a reverse direction when a shoe upper stitch count is reached to weave a second shoe upper facing the first shoe upper by knitting the two yarns (20 and 21) on the back needle bed along a second direction opposite to the first direction, weaving the first shoe upper in a reverse direction according to the shoe upper stitch count, and cyclically performing the above process to weave the first shoe upper along the first direction and the second shoe upper along the second direction; S12: weaving an extension (160 or 161) by knitting at least one of the yarns (20 and 21) when the shoe upper stitch count is reached in the previous step, continuing weaving in a reverse direction when an extension stitch count is reached while the extension (160 or 161) is woven, weaving the first shoe upper and the second shoe upper by knitting the at least two yarns (20 and 21) according to the shoe upper stitch count when the extension stitch count is again reached, and cyclically performing the above process to weave the extension (160 or 161), the first shoe upper and the second shoe upper, so that the extension (160 or 161) extends from where the first shoe upper and the second shoe upper are connected; and S13: cyclically weaving the first shoe upper and the second shoe upper by knitting the at least two yarns (20 and 21), and forming a shoe opening to complete the shoe embryo, wherein the extension (160 or 161) is one of a vamp decoration piece and an ankle strap of the shoe embryo, the extension is connected to a vamp section of the shoe embryo when being the vamp decoration piece, and the extension is connected to a heel section having the shoe opening of the shoe embryo when being the ankle strap.