Abstract: An experimental study on protons from a 7 m thick copper foil target irradiated by femtosecond laser pulses has been carried out. In the SILEX-Ⅰ femtosecond laser device, the proton energy spectra are measured at the different laser energies and laser power densities and at the same pulse width of 30 fs. Results show that the protons are emitted in the normal direction of the target back and have a certain cut-off energy. Along with the increase of the proton energy, the proton beams exponentially decay. For the same 7 m thick Cu target, the greater the laser energy is, the stronger the proton beam are. With the increase of the laser power density, the cut-off energy of protons increases.