The invention discloses a preparation method of a reinforced concrete beam with a demounting-free textile reinforced concrete (TRC) bottom mould, which relates to a long strip-shaped structural member for bearing. The preparation method comprises the following steps of: A, manufacturing a textile fleece reinforced concrete board: determining the size of the TRC board, and constructing a common steel mouldboard for the TRC board or customizing the steel mouldboard of the required size according to the size of the TRC board, preparing the textile glass fleece, mixing the concrete prepared according to the mass rate, grouting the concrete in the constructed common steel mouldboard or the customized steel mouldboard, paving the textile glass fleece, maintaining, and demounting the mould; and B, manufacturing the concrete beam with the demounting-free TRC bottom mould: constructing a common steel mouldboard for the TRC board or customizing the steel mouldboard of the required size according to the size of the TRC board, reinforcing bars, grouting the concrete, maintaining, and demounting the mould. The TRC board manufactured by using the method disclosed by the invention replaces the current wood mouldboard, the bamboo plywood mouldboard or the steel mouldboard, so that the defects that the current wood mouldboard, the bamboo plywood mouldboard or the steel mouldboard is not environmental-protection, is large in weight, high in price and low in construction efficiency, and can easily cause the conditions that the reinforcing steel bars cannot be accurately positioned and the surface of the member is not smooth after the mould is demounted, and the like can be overcome.