Abstract: The beam energy extracted from cyclotron is fixed, it is necessary to adjust it to meet different demands of different experiments. This study focuses on the feasibility of using thin film materials to change the beam energy. The ranges of 30 MeV α beams (extracted from cyclotron) in materials include diamond, aluminum and copper are calculated by the SRIM program, and the relationship between material thickness and the required beam energy is determined. The horizontal and vertical emittances of α beams, after being reduced to 9 MeV by interacting with different materials, are calculated by G4Beamline program. The following results are obtained: After penetrating the thin film materials, the size of beam spot approximately remained the same. The growth of beam transverse emittances is mainly caused by the increase of the divergence angles, among which the diamond film causes the least increase of beam emittance, and the root mean square value of the divergence angle is about 16 mrad. There is no significant dependency on the value of initial beam divergence angle (the root mean square value of initial divergence angle is less than 1 mrad). Vertical energy spread caused by different materials is about 1 MeV (FWHM) that is only determined by the final beam energy and has no connection with the kind of material. The more energy has lost, the greater the energy spread would be. Besides, the 30 MeV initial α beams interacting with thin film materials (diamond, copper, aluminum etc.) could produce about 10⁹/μA neutrons and γ particles, so radiation protection must be considered in practical applications.