The harmonic function was used to reverse the arc cam concave of EUP, MATLAB software was applied to carry out the cam profile curve一fitting，and the author analyzed the performance of fuel- sup- plied cam according to the fitting results. The results shows that N's value is limited, which the main rea- son for the truncation error in fitting process.We can increase the N's value to obtain a higher accuracy; when the equal velocity section is large, cycle fuel injection quantity is stable and rate of increase is also relatively stable.