The invention discloses a preparation method of a back junction N type solar battery, a back junction N type solar battery, a back junction N type solar battery assembly and a back junction N type solar battery system. According to the preparation method of the back junction N type solar battery, an N type crystalline silicon substrate is processed; a slotted structure penetrating a passivation film is formed on the back surface of the N type crystalline silicon substrate; aluminium paste is printed on the back surface of the N type crystalline silicon substrate, thus forming a back aluminium electrode; silver paste is printed on the back surface of the N type crystalline silicon substrate, thus forming a back silver master gate electrode; the silver paste is printed on the front surface of the N type crystalline silicon substrate, thus forming a front electrode; and sintering is carried out, thus forming the back junction N type solar battery. The method, the battery, the assembly and the system provided by the invention has the advantages that the passivation film on the back surface is slotted; the aluminium paste is printed; the aluminium paste forms partial contact with the p+ doped layer on the back surface, only at the location of the slotted pattern; compared with the method of printing the electrode by aluminium doped silver paste, the method provided by the invention has the advantages of improving the open-circuit voltage of the battery, greatly reducing silver paste consumption of the battery sheet and reducing the preparation cost of the battery sheet.