The invention discloses a preparation method of a bamboo-based composite material assembly type water storage container, which is formed by assembling bamboo-based composite plates. A sewage outlet is arranged at the bottom of a water container, a rainwater inlet and a water intake are respectively arranged above and below the side surface of the water container, a top cover is detachable to be convenient to be repaired and eliminate mud, and reinforcement cylinder hoops are arranged on a cylinder and gradually become dense from top to bottom. An assembly piece of the cylinder is a metal piece with adjustable assembly angle. The method has simple manufacture and field assembly time of only two days, and can be placed both on the ground and underground. The water container has the general service life of above 15 to 25 years and disposable economic forming about 100 to 150 yuan/m, and saves investment by 50 percent to 70 percent and the manufacture time by above 80 percent compared with a conventional water container. The invention has important practical significance for solving the problem of human livestock drinking water, and agriculture, small-sized processing industry as well as domestic and ecological water of a remote region lacking of water.