In this paper we discussed the relation between depth errors that happened in films growth and incidence angle variation on DBR reflectivity. We assume that there is 10% depth error in high and low index materials, and there are four plus one situations to be considered. Four are combinations of Hi +/- 10% error and Lo +/- 10% error, and no error. Our simulation results show that the depth error makes the reflective band shift and it almost doesn't reduce reflectivity. The thickness error of +/- 10% in (Al0.4Ga0.6N/GaN) DBR structure (15 pairs) at 420nm was 42mn. A theoretical analysis using Transfer Matrix Mode with MATLAB software on the influence of layer thickness and incidence angle variation in vertical-cavity surface-emitting lasers with distributed Bragg reflectors (DBRs) on lasing wavelength is presented. It is shown that changing the thickness of the layers in the DBR mirror by only 10% is sufficient to produce shifts in the peak reflectance wavelength up to +/- 20 nm (for a blue laser at 420nm). This could limit the precision of a desired wavelength, which is its reproducibility.