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. <EOS>