With the help of traditional paraffin-section method, the structure, distribution, initiation and development of resin ducts of the primary structure of stem in Pinus massoniana were investigated. The results were as follows the resin ducts were found in both cortex and primary xylem. At the level 390 micrometer from the shoot tip, a group of the cortical duct initials developed from the ground meristematic cells which are located at both sides of the procambium bundle. The development can be divided into 5 stages the initial stage, the intercellular layer swelling stage, the intercellular space forming stage, the duct expanding stage and the mature stage. In the primary xylem, the duct initial cells developed from the procambium cells. The style of development was similar to that of the resin ducts of cortex. The difference of structure between two kinds of resin ducts in stem primary structure and the reason for delaying initiation of cortical resin ducts in P. massoniana, compared with P. tabulaeformis, were analyzed and discussed.