In order to improve the accuracy of the traditional laser tracking interferometric measurement method and make the datum traceability more reliable, an optimization method of datum measurement in multiple attitudes is proposed in this paper. The method firstly constructs a multi-attitude datum layout on the basis of the traditional laser tracking interferometry, and collects measurement information in different datum directions by laser tracker, and then uses a weight-based measurement result optimization strategy to optimize the combination of measurement data, and then outputs the measurement results and performs error source analysis and uncertainty evaluation. The experimental analysis of the reference ruler based on this optimization scheme and the comparison with the higher accuracy CMM method, the En value is 0.1, which verifies the reasonableness of the uncertainty assessment, and the experimental comparison shows that the reference length output by the multi-attitude measurement optimization scheme is more reliable than the single attitude. The optimized method provides a new calibration scheme for realizing the measurement traceability of high-precision large-size datum rulers, which has a good practicality and certain guiding significance.