According to the completeness theory of circuit, Chua [Chua L O 1971 IEEE Trans. Circ. Theor. 1971 18 507] put forward the fourth basic circuit element memristor besides resistor, inductor and capacitor in 1971. And memorisistance is defined as the ratio of the flux to the charge passing through it. With the emergence and development of nanoscale semiconductor technology, HP laboratoty successfully fabricated a physical memristor in 2008. The successful fabrication of memristive device caused a stir in the whole electronic field and thus a vast number of researchers were involved in the research, owing to its superior properties, i.e., nanoscale dimension, continuous input and output property, switching characteristics and unique non-volatile memory capacity. With all these extraordinary properties, memristors possess many possibilities for the development of future integrated circuits and analog computer. With the gradually in-depth study of memristor, memristor is being microsized, and its internal structure, motion law among its internal particles and influences resulting from the parameters are further explored. In recent years, the memristor has made significant achievement in the areas of non-volatile solid-state memory, intelligent storage, very-large-scale integrated circuitry, programmable analog circuits, and artificial neural networks. So far, the influence of size parameter on the memristor has been little studied, although the size parameter is one of the key factors in the memristor fabrication technology, which severely restricts the memristor development and its practical application. In the paper, we theoretically analyze the influences of size parameter on two practical memristor models (i.e., the HP memristor and spintronic memristor) in detail based on the Ohm’s law. On this basis, a series of circuit experimental simulation is carried out, and the corresponding memristor characteristic curves are thus obtained. Furthermore, we choose 4 most representative experimental results, and make specific analysis on them. Those results indicate that the optimal length of HP memristor is in a range from 8 nm to 12 nm, while the proper range of spintronic memristor is from 500 nm to 600 nm. The final results can not only contribute to memristor physical implementation and its applications, but also provide theoretical references and reliable experiment basis for the further development of the titanium oxide memristor devices and the relevant research.