Based on the brief discussion of error propagation in multivariate calibration and analysis, the flexible tolerance simplex method (FTSM) was applied to analyze vitamin B1, B2, B6 and niacinamide simultaneously. The results obtained were comparatively satisfactory both in precision and in accuracy. The average recoveries of vitamin B1, B2, B6 and niacinamide were 99.8 +/- 0.9% (CV), 100. 1 +/- 0.8% (CV), 100.2 +/- 2.1% (CV) and 100.1 +/- 0.7% (CV) respectively. All these show that FTSM, with calibration matrix K calculated from K = ASCST (CSCST)-1, is one of the most efficient procedures for improving accuracy, especially when there are interactions between variables and the problem is ill-conditioned.