Nanoscale memristors open up new opportunities for the development of brain neural networks. Simple and precise memristors enhance the performance of various neural networks and operational circuits. In this letter, a three-terminal memristor is proposed, which makes the memristor more flexible and practical in circuit design and application through the introduction of a control port. Consid-ering that the resistance of a three-terminal memristor consists of three parts, i.e., metal region, low-resistance region, and high-resistance region, a three-segment piecewiselinear method is applied to fit these three regions. The model of this memristor is constructed through the derivation of the memristor formula and working principle. Candence simulations are conducted on the resultant circuit to verify its correctness.