The angle straggling and energy straggling of 12C6+ beam were simulated with method of Geant4. And the energy of 12C6+beam ranged from 80 MeV to 360 MeV per nucleon, while the mass thickness of the target, PMMA,Al,Cu,Pb, ranged from 0.5 g/cm2 to 4.0 g/cm2. Besides, the Bragg peak of 12C6+ beam which have passed through range shifter was compared to the Bragg peak of mono\|energetic 12C6+ beam. The results of the simulation show that the energy of 12C6+ beam is higher, the thickness and atomic number of the target is lower, then the angle and energy straggling of 12C6+ beam after range shifter is lower, the effect of its Bragg peak is minimal. So, in the case of only consider the angle and energy straggling, the target of lower atomic number is more suitable for range shifter.