21 tinning bronze samples were observed and analyzed by optical microscope, petrography microscope, scanning electron microscope (SEM), X - ray energy dispersive spectrum meter (EDS ) and X - ray diffraction (XRD) instrument. The samples unearthed from Guyuan of Ningxia province, Chengdu and Mianzhu of Sichuan province and Yunnan province were dated to the fifth - second century B.C. The results show that although the samples came from different regions, they have some common characteristics as follows, (1) The tinning layers with different thicknesses were existed. (2) The layers shown casting structures and hot tinning appearances. (3) Tin content of the layers was very high. (4) Cu41Sn11 and other Intermetallic compounds as well as SnO2 were main substance in the layers. Some imitating experiments of hot - tinning were carried out in laboratory. Basing on the results of experiments and the analysis of tinning layers, it is suggested that the formation of the tin-rich layers was by hot-tinning method and several ways for tinning processes, such as hot-dip and hot-wipe etc. By comparing thickness, microstructure and phases in the tinning layers of bronzes came from above three different regions, it is found that some differences were existed between Yunnan and the other two regions, indicating they probably used different hot-tinning processes. A discussion about initial use and diffusion of tinning techniques in ancient China is made in this paper.