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We propose a method based on modal interference in a birefringent optical fiber for distributed strain measurement. A frequency-modulated optical signal from a laser diode was launched in a birefringent fiber whose 'V ' number was set in the range 2.405-3.831. The beat signal produced due to the interference of two lower order modes LP 01 and LP 11 was detected in a photodetector. The change in propagation constants between two modes under loading conditions leads to a phase variation of interference signal. The amplitude of the beat frequency was measured in the frequency domain by varying the modulating frequency, and it provides the measurand distribution along the beam. Results for strain distribution of a simply supported beam (51.0 cm × 3.0 cm × 0.6 cm) for an applied load of 250-1500 g are presented.