The invention discloses a preparation method of unbleached neosinocalamus affinis paper pulp, and belongs to the technical field of pulping and papermaking. The whiteness of paper pulp prepared from neosinocalamus affinis is 25%-40% ISO, the tensile index is larger than or equal to 8 Nm/g, the folding strength is 15-140 times, the fracture length is 6-8 km, the ash content is smaller than or equal to 1.2%, the breaking length is 150-600 mN, and the beating degree is 16-22-degree SR. The preparation method of the neosinocalamus affinis paper pulp comprises the following steps of raw material repulping, steaming, deflaking, pulp grinding, screening and washing. The neosinocalamus affinis paper pulp can be used for preparing household paper. The paper pulp preparation method has the advantages of being high in yield, easy to operate, convenient to produce, low in cost and environmentally friendly, and 100% of the natural color of the neosinocalamus affinis is kept.