In this work, the influence mechanism of the initial state of Ti–Si3N4 system on the prepared composites was explored, and the treatment which changes the size of Si3N4 and ball-milled Ti–Si3N4 system was carried out. It is found that the large Si3N4 particles (20 and 50 μm) tend to form more core-shell particles in the composite, and the synthesized TiN particles tend to aggregate around core-shell particles. When the size is small (2 μm), Si3N4 tends to bind to each other, and the TiN will grow synergically and connect to form aggregations. However, the distribution of TiN can be improved by ball-milling Ti–Si3N4 powders for an appropriate time, and the dispersion of the enhanced phase will be more difficult when the optimal ball-milling time is exceeded. It is proved that in the vacuum environment, where the ball-to-weight is 6:1 and the milling speed is 300 rpm, ball-milling for Ti–Si3N4 mixed powder with 6 h can effectively promote the uniformity of microstructure of the prepared TiN–Ti5Si3 reinforced Cu matrix composites.