We investigate the universality class of Bruinsma-Aeppli (BA) model in two dimensions. This model is consisting of two coupled XY order parameters, six-fold and two-fold symmetry, and is proposed to describe the Smc-A to Hex-B transition in some Smectic liquid crystal compounds. Using high resolution Monte Carlo simulation technique based on multi-histogram method and cluster algorithm, and also finite size scaling, we compute the critical exponents of this model with high accuracy. We find that for some ranges of coupling constants this model undergoes transition from disordered phase to a symmetry broken phase with both hexaitc and herringbone orderings.