The invention discloses a power generation method based on osmotic pressure and a battery. The power generation method comprises the following steps: S1, the cyclic movement of electrolyte solution isconstructed; in S1, a water tank is set up and is separated by semi-permeable membranes into three regions A, B and C, electrolyte solution is added to the regions A, B and C, polymer material solution is added to the region B, and the polymer material in the polymer material solution cannot pass through the semi-permeable membranes; the osmotic pressure of the liquid in the region B is high, andthe liquid level in the region B is higher than the liquid levels in the regions A and C due to the effect of osmotic pressure; and the height of liquid level in the region B is recorded as hB, the height of liquid level in the region A is recorded as hA, the height of liquid level in the region C is recorded as hC, and hB>hA=hC; and S2, a magnetic field is arranged, wherein the magnetic field covers the region B and is slightly larger than the region B, the upper edge of the magnetic field is higher than the water surface in the region B, the lower edge of the magnetic field crosses the bottom of the water tank, and most of the regions A and C are not in the magnetic field. Power is generated under the action of osmotic pressure and under the action of gravity field.