Graded Ti-6Al-4V alloys were produced by selective laser melting (SLM). Regulation of laser power and scanning speed was applied separately on each sample along the building direction. The microstructure transformation and phase transition in the graded Ti-6Al-4V were investigated. Results show that due to the rapid cooling rate of the SLM process, the microstructure of Ti-6Al-4V is mainly acicular α′ martensite in prior β column grains. The β column grains are enlarged with the increase of laser power or the decrease of scanning speed. The preferential orientation of α′ grains changes due to the variation of laser power and scanning speed. Moreover, the ascending scanning speed or descending scanning speed during the process may lead to two different defects.