Abstract: To improve the sensitivity of flexible conductive rubber-based resistance sensors (RSs), RSs fabricated with conductive rubber were designed and their resistance responses to cyclic strain loads were carried out and the corresponding mechanism was analyzed. Ethylene polydimethylsiloxane (3450) was selected as the substrate layer of the sensor due to its good stiffness. Conductive silicon rubber (CSR) with carbon fiber (CF) filled in polydimethylsiloxane (PDMS) was used as the conductive layer based on its good mechanical and electrical properties. Two kinds of flexible RSs with different printed pitches were manufactured with a 3D printing process. The resistance responses of the RSs were tested on the cyclic tensile loads with strain variables of 30%, 60%, 90% and 120% and loads of different tensile strain rates, respectively. Changes of internal CFs in CSR were observed with the aids of microscope and equivalent circuit model and fitting formula of RS were established. Results show that the resistivity changes of the RSs are obvious when the strain is 60%-120%, especially for the fine-pitched RS-2, and their responses are insensitive to the strain rate. The observed changes of internal CFs during the stretching process implies that with the increase of spacing between the fibers, the tunneling resistance increases exponentially, which agrees with the fitting results of tested resistance change of the RS. It is also consistent to the elbow flexion-extension motion and long-term cyclic mechanical strain loading. The fabricated CSR-based RS with high sensibility and stability is potentially applicable in motion tests.