The invention discloses a sample observation surface flattening device for a microscope, which comprises a seat body and a pressing plate. The seat body comprises a base. The upper surface of the base is a flat plane. The lower surface of the pressing plate is also a flat plane and is always parallel to the upper surface of the base. The pressing plate is movably connected with the seat body, so that the pressing plate takes linear motion in a direction vertical to the upper surface of the base and the lower surface of the pressing plate is always kept parallel to the upper surface of the base. The invention also discloses a sample observation surface flattening method in which the device is employed. The sample observation surface flattening device for the microscope and the flattening method, which are disclosed by the invention, are simple and applicable to operate. An observation surface of a sample obtained by pressing has good levelness. The problem of unclear observing mirror image of the microscope, which is caused by the inclination, is avoided, and the observing effect of the microscope is greatly improved. Moreover, the samples with various sizes can be flexibly pressed according to the sizes of the samples so as to obtain the observation surfaces with good levelness. The sample observation surface flattening device for the microscope and the flattening method are suitable for any sample preparation treatment with high requirement on the levelness.