The invention provides a method for performing one bath of ramie fiber preparation and chemical modification. The method comprises the steps of: firstly, blending peroxide, sodium tripolyphosphate, urea, peroxide stabilizer, a penetrant and water into degumming solution; then mixing raw ramie with the degumming solution according to the mass ratio of 1:1, increasing the temperature and holding the temperature, and removing a part of gum; and finally, adding chemical modifier into the raw ramie and degumming solution mixture, increasing the temperature, boiling off, thoroughly removing gum to obtain the chemically modified textile ramie fibers. The method overcomes the deficiencies of the prior art, is simple in flow process, the original three procedures are combined into one bath solution, so that the total reaction time is shortened, the washing procedure in the middle link can be omitted, the energy consumption can be greatly reduced, the pull rate is improved, the breaking strength, the breaking elongation rate, the flexibility, fineness properties of the special ramie fibers can be obviously improved, and the performance index can achieve the ramie spinning requirement.