The strain and temperature dependencies of a step-index single-mode–multimode–single-mode (SMS) fiber structure are investigated numerically and experimentally. For intensity-based strain measurement using a single SMS fiber structure, at a selected wavelength, it is found that there is a high strain dependence, but also a temperature dependence that will induce strain measurement error. To minimize the temperature-induced strain measurement error, two SMS fiber structures are proposed and demonstrated in a ratiometric power measurement scheme; one SMS structure acts as the strain sensor, and the other SMS structure acts as the temperature monitor. The extracted temperature information is used to determine a strain value based on a suitable calibration of strain responses with temperature variations. It is demonstrated that for strain measurement from 0 to $1000\mu \epsilon$ within the temperature range from $10°\mathrm{C}$ to $40°\mathrm{C}$ , the proposed configuration can provide a strain and temperature resolution of $0.34\mu \epsilon$ and $0.14°\mathrm{C}$ , respectively, with a temperature-induced strain measurement error as low as $0.39\mu \epsilon$ .