The invention provides an electrode subassembly, a preparation method thereof and a lithium secondary battery. The electrode subassembly is composed of a positive plate, separating layers and negative plates. The positive plate is a continuous positive plate; the two surfaces of an anode current collector of the positive plate are coated with an anode active material; and the positive plate is folded continuously so as to obtain a Z-shaped vertical section. The two surfaces of a cathode current collector of each negative plate are coated with a cathode active material, and are respectively arranged to be opposite to two positive plate opposite surfaces which are formed because of folding, so that the two negative plate surfaces which are coated with the cathode active material are respectively opposite to the two positive plate surfaces which are formed by folding, but positive plate outer surfaces which are formed by folding are not opposite to the surfaces of the negative plate. Each separating layer is arranged between a surface of the positive plate and a surface of a negative plate, wherein the surface of the positive plate and the surface of the negative plate are arranged oppositely. The positive plate and the negative plates are respectively provided with a contact area used for connection of lead wires. The electrode subassembly is easy for preparation, and is suitable for large-scaled production; materials are fully used; and cost is reduced.