Abstract: The wetting behavior of molten Sn0.3Ag0.7Cu (SAC)-xTi (x=wt.%) on the surface of monocrystalline Si at 800−900 ℃ was studied under high vacuum by the modified drop method. The results show that SAC-xTi/Si system belongs to the inert wetting system, and the Ti addition improved wettability, significantly. Without Ti addition, the system achieved the equilibrium contact angle of 63° after 1 800 s at 800 °C; With 1% Ti addition, the system achieved the lowest equilibrium contact angle of 41° after 1 800 s at 900 °C; With 3% Ti addition, the system achieved the fastest spreading in 50 s at 900 °C. The wetting mechanism is that the active component Ti accelerates the removal of oxide film on the surface of monocrystalline Si. During the spreading process of the molten solder, the temperature-dependent “pyramid” microstructure was formed at the solid/liquid interface through dissolution-reprecipitation mechanism and micro-mask mechanism, i.e., the higher temperature induced the sparse and larger “pyramid” microstructures. The appearance of “pyramid” microstructures did not improve the wettability of the system, on the contrary, the wettability became worse due to the pinning of the triple line.