As an additive manufacturing technology, selective laser melting (SLM) process can solve the manufacturing difficulty of Ti-5Al-2.5Sn (TA7) easily. But the low building efficiency of SLM retards its wide applications in aviation, petrochemical and other fields. In order to solve the above problem, the influence of layer thickness on relative density, microstructure and mechanical properties of SLMed TA7 samples were studied in this work. The results show that when the laser power and hatching space are constant, the relative density gradually increases with the decrease of the laser volume energy density under the layer thicknesses less than or equal to 40 μm, whereas first increases and then declines with the decrease of the laser volume energy density under the layer thicknesses larger than 40 μm. At the same time, with the increase of layer thickness and the decrease of scanning velocity, the cooling rate gradually decreases during the SLM processing, when the cooling rate is lower than 6.8×10⁷ K/s, the microstructure will gradually transform from acicular martensite α' to massive α_m. Through the optimization of SLM parameters, the dense TA7 bulk specimens with higher microhardnesses, yield strengths and ultimate strengths in comparison to the as-cast and deformed TA7 alloys can be obtained under all layer thicknesses (20~60 μm). While when the layer thicknesses are not larger than 40 μm, the ductility of the SLMed TA7 is also superior to that of the as-cast TA7 and comparable to that of the deformed TA7. Finally, the optimal layer thickness and combination of SLM process parameters are successfully determined to balance the building efficiency, metallurgical quality and mechanical properties of the TA7 alloy parts.