The theory analysis and experiments of multimode fiber (MMF) temperature sensors with the capability of wavelength encoding are presented. The analysis based on multimode-interference predicts the characteristic dip-wavelength positions of the MMF sensor according to the radius, the length and the refraction index of the MMF. It is used to optimize the sensor to produce only one characteristic dip-wavelength for a MMF temperature sensor in the wavelength range of a broadband source ASE. Three MMF temperature sensor heads with the length of 4 cm, 5.5 cm and 10 cm, packaged by a micro-silicon-tube, are fabricated and tested based on the ASE source with the wavelength range from 1525 nm to 1565 nm and optical spectral analyzer with the resolution of 0.01 nm separately. MMF temperature sensors with only one dip-wavelength and the temperature sensitivities ～13 pm/℃ are gained, which agrees with the theoretical analysis well.