A control method of a water-saving washing machine having a vertical axis of which a locking hole and a drainage port are formed in the bottom of an inner tub of the washing machine, and a locking mechanism and a drainage control mechanism are arranged at the bottom of an outer tub of the washing machine, the control method comprising: Step I: carrying out a washing/rinsing procedure, a master control board controlling the locking mechanism to couple with the locking hole to lock the inner tub, and the drainage control mechanism blocking off the drainage port, supplying water to the inner tub of the washing machine until a set water level or water volume is reached, starting washing, wherein water is absent between the inner tub and the outer tub; Step II: carrying out a drainage procedure after the washing/rinsing procedure ends up, the master control board controlling the drainage control mechanism to open the drainage port, and water in the inner tub being drained through the drainage port; Step III: carrying out a dewatering procedure after the drainage procedure ends up, the master control board controlling the locking mechanism to release the inner tub, and to drive the inner tub to rotate for dehydration; wherein the control method further comprises: arranging a locking rod to be a diameter-variable cylinder, arranging a position switch at the locking mechanism corresponding to an outer side of the locking rod, after the locking rod sticks into the locking hole in place and the locking rod is subjected to restoring, portions with different diameters of the locking rod correspond to a contact of the position switch and trigger the position switch to send out corresponding signals. Step I: carrying out a washing/rinsing procedure, a master control board controlling the locking mechanism to couple with the locking hole to lock the inner tub, and the drainage control mechanism blocking off the drainage port, supplying water to the inner tub of the washing machine until a set water level or water volume is reached, starting washing, wherein water is absent between the inner tub and the outer tub; Step II: carrying out a drainage procedure after the washing/rinsing procedure ends up, the master control board controlling the drainage control mechanism to open the drainage port, and water in the inner tub being drained through the drainage port; Step III: carrying out a dewatering procedure after the drainage procedure ends up, the master control board controlling the locking mechanism to release the inner tub, and to drive the inner tub to rotate for dehydration; wherein the control method further comprises: arranging a locking rod to be a diameter-variable cylinder, arranging a position switch at the locking mechanism corresponding to an outer side of the locking rod, after the locking rod sticks into the locking hole in place and the locking rod is subjected to restoring, portions with different diameters of the locking rod correspond to a contact of the position switch and trigger the position switch to send out corresponding signals. arranging a locking rod to be a diameter-variable cylinder, arranging a position switch at the locking mechanism corresponding to an outer side of the locking rod, after the locking rod sticks into the locking hole in place and the locking rod is subjected to restoring, portions with different diameters of the locking rod correspond to a contact of the position switch and trigger the position switch to send out corresponding signals.