The invention discloses a whole bamboo board flattening method. A ripe bamboo grown naturally is taken, one to three bamboo internodes are selected, protruding parts of the bamboo internodes with bamboo joints need to be ground, bamboo inner skins and bamboo outer skins do not need to be removed, internode softening treatment is conducted, then compression treatment in the circumferential direction is conducted, the internodes are placed and taken out after being naturally aired, the compressed internodes are flattened to be in a C shape or in an arc shape and extruded into bamboo boards flattened completely, the bamboo boards are subjected to fixing treatment and taken out after being subjected to depressing drying, and the bamboo boards which are flattened completely and are not deformedare obtained. Cracking or fracturing is not liable to occur to the bamboo boards obtained through the method, the original strength and toughness of the bamboo internodes are reserved, the product quality is improved, the bamboo boards can be used for construction materials (such as floors and wallboards) and can also be used for craft materials, the application range of bamboos is enlarged, andthe additional application value of the bamboos is increased.