The mechanism of temperature effect on fiber length by heat expansion and cold contraction effect have been analyzed theoretically. Experimental verifications have been carried out by different lengths in different wavelengths. Experimental results show that in different wavelengths, single-mode fibers of different lengths change little per km when the variation of temperature is 1 ℃. For fibers of different lengths, when the variation of temperature is 1 ℃, the variation of single-mode fiber length is proportional with fiber length, which is consistent with theoretical analysis results.