A new method to measure the beat-length of polarization maintaining fibers is presented. The key components of the all-fiber measuring system are a broadband light source and two broadband fiber circular polarizers. Theoretical analysis shows that, compared with the polarization interference system made up by fiber linear polarizers, circular polarizers can eliminate the influence of the angles between the axis of polarization maintaining fibers on the visibility of the interference fringe. The beat-length of a panda polarization maintaining fiber is investigated for verification. Experimental results are in good agreement with the theoretical analysis. The accuracy and repetition of beat-length measurement are 0.1 mm, and the visibility of the interference fringe is better than 0.9. Since there is no need for accurate angle adjustment between polarization maintaining fiber devices, the measurement system has the advantages of simple structure and low operation requirement.