A method for making heated plane of a cooler obtain better flatness and roughness includes a grinder with a grinding plate and a fixture. Then, the cooler is arranged onto the fixture. Next, the abrasive is injected into the gap between the grinding plate and the heated plane, making the fixture press and clamp the cooler in a way, such that the heated plane of the cooler contacts the abrasive closely. Finally, the grinding plate is rotated to make at least one grinding process to the heated plane, making the heated plane obtain a surface with better roughness and flatness, further enhancing the contact tightness between the heated plane and a heating element, and therefore promoting the thermally conductive efficiency between the cooler and the heating element.