Concentrated heavy precipitation has a great potential to cause severe flood disasters, especially in densely populated areas. However, the influencing factors of the spatio-temporal changes of precipitation concentration have not been well understood and the relationship between the characteristics of precipitation concentration and the structure of precipitation has rarely been investigated so far. This study explored the concentration characteristics of precipitation based on the Gini coefficient and further investigated the relationship of the precipitation concentration with the precipitation structure by means of a set of precipitation indices based on the daily precipitation data from 1960 to 2014 in the climatic transition zone of the Huai River basin (HRB), China. Results show that: (1) There is a non-significant upward trend for the Gini in the HRB. The mean of the Gini coefficient shows a spatial pattern of increase from the south to the north, and the standard deviation (SD) of the Gini shows a pattern of increase from the northeast to the southwest. (2) The composite mean of the Gini in the drought years is larger than that in the flood years for all the stations. And the composite SD of the Gini in the flood years is larger than that in the drought years for most of the stations. (3) The non-significant increase of the Gini in the HRB is mainly associated with AR (Annual rainfall), RD (Rainy days), the light and moderate rainfall (mainly PF20, PF40, PF50) and the wet-day and dry-day indices (PPWW, PWSAV, PPDD and PDSAV).