The present invention discloses an assembled bamboo sleeper, which is obtained by using a bamboo unit as a raw material, dried and modified at the temperature of 110-180 C., undergone coating treatment using a dopamine solution, adhesive dipping, curing and solidifying, assembling and gluing, further solidifying, further treatment using a dopamine solution, and anti-mildew and/or anti-corrosion and/or anti-insect treatment, and then fastened. The present invention further provides a preparation method for the foregoing bamboo sleeper. The bamboo sleeper prepared in the present invention is green and environmentally friendly, and applicable for ballasted tracks of railways and urban rail transit systems.