For the growth of AlN crystal by PVT method in nitrogen environment, the growth rate is different due to the different surface chemical properties between Al-polar and N-polar. And differentiated growth behaviors were observed within these surfaces due to the disparate migration behaviors of atoms. AlN growth on Al and N surfaces were carried out under the same conditions, i.e., growth temperature, thermal gradients, pressure, seeds and in the same apparatus. With the purpose of evidently exhibiting the discrepancy of Al and N surfaces, an Al-N growth within one growth cycle was realized by turning half of the seed crystal. For the Al-polar growth, domain boundaries merely within the well-grown planes were found. While for the growth on N surface, morphologies with well-aligned steps were observed, and grain boundaries are covered by these steps at the secondary growth.The growth step of Al surface is smooth but obstructed by defects, and the domain development is obviously independent of each domain growth which were further observed by AFM. The growth step of N surface is not regular but more continuous than that of Al surface, and the continuous growth step (or step cluster) also appears at the original boundary of crystal domain. Consisted with the XRD results, it can be figured out that, N growth is an effective approach to obtain an improved crystalline quality for AlN seeds with lower crystallinity.