Tool wear and friction coefficients have a big impact on the cutting force and surface quality. To study the effect of tool wear and friction coefficients on cutting force， an cutting force model was developed， taking into account tool wear and variable friction coefficients. First， the edge radius for worn tool was looked at. It was shown that the edge radius gets bigger as the tool wears down. Next， the minimum cutting thickness for worn tool was explained. It was thought that the minimum cutting thickness gets bigger as tool wear and edge radius get bigger. Lastly， the cutting of Al alloy was researched by single crystal diamond tool， and compared the variations in cutting force with respect to cutting depth， feed speed， tool edge radius， tool wear width， and constant and variable friction coefficients. It was shown that the normal and tangential cutting forces increase with increasing depth of cut and feed rate. When the edge radius went from 150 nm to 450 nm， the tangential force went up by 1.13 times and the normal force went up by 2.12 times. When the tool wear width went from 0 to 0.55 μm， the tangential force went up by 1 time and the normal force went up by about 7 times， and the constant friction coefficient model has a maximum error in cutting force of 41%， whereas the variable friction coefficient model has a maximum error within 11%. Hence， the cutting model， which accounts for both tool wear and changing friction coefficients， aligns more closely with the real cutting process.