The invention belongs to the technical field of calcium silicate board preparation, and relates to a preparation method for a calcium silicate board blank, a preparation device, a preparation method for a calcium silicate board and the calcium silicate board. The preparation method for the calcium silicate board blank comprises the following steps: conveying prepared slurry to a pre-forming devicethrough a feeding device; performing vacuum dehydration in a pre-forming process by using the pre-forming device, and enabling a dehydrated material to be adhered to a feeding blanket under the action of the pre-forming device; enabling a material layer on the feeding blanket to be rolled on a forming cylinder under the drive of a transmission mechanism, press-forming by the forming cylinder while the number of rolling layers reaches the requirement, and preparing the calcium silicate board blank. The preparation method is capable of solving an existing technical problem in a traditional production technology that the large-scale, ultra-thin and/or ultra-thick calcium silicate board cannot be produced.