A transmission mechanism for an electric drill, wherein the transmission mechanism comprising: a primary planet carrier having a plurality of primary planetary gear shaft arranged at one end thereof and a sun gear arranged at the other end thereof; a gear assembly comprising a primary gear ring and a primary gear set located in the primary gear ring; a secondary planet carrier comprising a plurality of secondary planetary gear shafts arranged at one end thereof and an output shaft arranged at the other end thereof; and a secondary gear assembly comprising a secondary gear ring and a secondary planetary gear set located in the secondary gear ring, characterized in that; the primary gear set comprises at least two primary planetary gear sets; the at least two primary planetary gear sets are pivotably mounted on the primary planetary gear shaft, an outer side of the primary planetary gear sets engage with the primary gear ring, and an inner side of the primary planetary gear sets engage with a central gear arranged on a motor output shaft; wherein, the secondary planetary gear set is pivotably mounted on the secondary planetary gear shafts, an outer side of the secondary planetary gear set engages with the secondary gear ring, and an inner side of thereof engages with the sun gear, wherein the transmission mechanism further comprises a gear box receiving the primary gear assembly and the secondary gear assembly; wherein the gear box comprises assembling holes (1514, 1522); wherein a fixing portion (1212, 1412) is arranged on side walls of the primary gear ring and the secondary gear ring respectively and extends axially throughout the thickness of the primary gear ring and the secondary gear ring respectively; and wherein the assembling holes (1514, 1522) and the fixing portion (1212, 1412) cause the primary gear assembly and the secondary gear assembly to be secured in the gear box through fasteners, wherein a fixing plate is arranged on an end of the primary gear assembly away from the secondary gear assembly so as to limit the primary planetary gear sets in the primary gear ring, and wherein the fixing plate comprises a main body and an elastic resisting portion extending from the main body, and wherein the elastic resisting portion elastically abuts against the side wall of the gear box. a primary planet carrier having a plurality of primary planetary gear shaft arranged at one end thereof and a sun gear arranged at the other end thereof; a gear assembly comprising a primary gear ring and a primary gear set located in the primary gear ring; a secondary planet carrier comprising a plurality of secondary planetary gear shafts arranged at one end thereof and an output shaft arranged at the other end thereof; and a secondary gear assembly comprising a secondary gear ring and a secondary planetary gear set located in the secondary gear ring, characterized in that; the primary gear set comprises at least two primary planetary gear sets; the at least two primary planetary gear sets are pivotably mounted on the primary planetary gear shaft, an outer side of the primary planetary gear sets engage with the primary gear ring, and an inner side of the primary planetary gear sets engage with a central gear arranged on a motor output shaft; wherein, the secondary planetary gear set is pivotably mounted on the secondary planetary gear shafts, an outer side of the secondary planetary gear set engages with the secondary gear ring, and an inner side of thereof engages with the sun gear, wherein the transmission mechanism further comprises a gear box receiving the primary gear assembly and the secondary gear assembly; wherein the gear box comprises assembling holes (1514, 1522); wherein a fixing portion (1212, 1412) is arranged on side walls of the primary gear ring and the secondary gear ring respectively and extends axially throughout the thickness of the primary gear ring and the secondary gear ring respectively; and wherein the assembling holes (1514, 1522) and the fixing portion (1212, 1412) cause the primary gear assembly and the secondary gear assembly to be secured in the gear box through fasteners, wherein a fixing plate is arranged on an end of the primary gear assembly away from the secondary gear assembly so as to limit the primary planetary gear sets in the primary gear ring, and wherein the fixing plate comprises a main body and an elastic resisting portion extending from the main body, and wherein the elastic resisting portion elastically abuts against the side wall of the gear box.