The invention relates to the field of sewing machines, and mainly discloses a main unit of a sewing machine. The main unit of the sewing machine comprises a spindle, a transmission gear and a hand wheel, wherein the transmission gear is fixed on the spindle in a sleeving manner and located in an inner cavity of a casing; the hand wheel is fixed at one end of the spindle in a sleeving manner and located outside the casing; the spindle is fixed on the casing through a first fixing sleeve and a second fixing sleeve; the second fixing sleeve is fixed on the spindle in an internal sleeving manner and is sleeved with a bearing; the bearing is sleeved with the first fixing sleeve; a bearing seal assembly is arranged between the first fixing sleeve and the casing; a spindle seal assembly is arranged between the first fixing sleeve and the spindle; and the first fixing sleeve and the spindle seal assembly are adjacent to the hand wheel. The main unit of the sewing machine has the positive effects as follows: through structural improvement of the main unit of the sewing machine, lubricating oil in the inner cavity of the sewing machine is effectively prevented from leakage.