In this paper, a design method for the yarn tension sensor based on surface acoustic wave (SAW) is presented. When the yarn tension is applied to the sensor's doubly-clamped beam (i.e., piezoelectric substrate), it is linearly related to output frequency shift, which achieves the purpose of measuring yarn tension. This paper deduces the functional relationship between the oscillation frequency shift of the sensor and the yarn tension. We put forward the choice of piezoelectric substrate material, the choice of the piezoelectric die size and the placement of interdigital transducers (IDTs) as the three key issues to be determined. By using the ANSYS software, we determined that the optimal piezoelectric substrate is quartz, and that the optimal size of the die, and the maximum strain area of the die. When IDTs are placed in the maximum strain area of the piezoelectric substrate, the sensor has the best sensitivity. We have designed and produced the sensor, and also have tested the sensor. Experimental results: the range is 0~2 N, the linearity is 1.0112%, the hysteresis is 0.6153%, the repeatability is 1.1067%, the accuracy is 1.6205%, the maximum overload capacity is 200% (i.e., 4 N), and the fracture strength of the substrate is 5 N.