The Composites are difficult machining materials which widely used in aerospace industry due to their excellent mechanical properties. Tool wear and delamination are considered the major concern in manufacture the parts and assembly. The orthogonal experiment method was used to investigate the milling force of carbon fibred composite with diamond mill tool. The experiments were carried out under air cooling cutting conditions. The experimental results indicated that the feed rate was the most significant fact which affect the average peak value of the milling force. the average milling force decreased with the cutting speed increased and increased with the feed rate and width of cut increased.