The wettability of rock is a combined effect of rock, crude oil and water. It has direct impact on the distribution of the fluid in the reservoir and determines the degree of difficulty of the fluid percolation. Reservoir rock wettability research is of significance to determine a reasonable flooding way and enhanced oil recovery. In order to find out the carbonate reservoir core wettability and its influencing factors, Amott method was used to measure the wettability and imbibitions recovery degree of carbonate rocks and the wettability changes of carbonate rocks after steam flooding. At the same time, in order to do qualitative test for the wettability of carbonate rocks,the oil-water flowing experiment under both reservoir and high temperature(150 ℃) was carried out. The results show that: the carbonate reservoir core is oil wetting or weak oil wetting, and the reservoir seepage resistance is high, which is different from the ordinary sandstone reservoir’s water wetting characteristics; studies suggest that the rock mineral composition and the different constituents of crude oil are the main reasons that cause the differences; steam flooding could cause the decrease of carbonate rocks wetting index to improve the rock’s wettability at certain extent, and also the reservoir’s seepage. The oil-water relative permeability experiment on this core further proved the conclusion. This understanding can provide a theoretical basis for the optimization of development schemes.