A new method is introduced in this paper for calculating alpha particle energy versus traveled distance (APETD) in air as emitted from 241Am and 230Th sources as well as the alpha range versus its energy and its energy versus distance. This method is to derive the stated relevant equations and in particular to speed up the calculation of E(x) by a Monte-Carlo simulation. By a fitting procedure, an analytical formula E(x) was determined in terms of a series of powers of distance x. Then a randomly sampled x can be quickly transformed into a corresponding energy E. The APETD calculations were run on a Microsoft Windows 7 32 bit operating system with a maximum usable memory of 3 GB. The results of calculations for alphas of the above two radionuclides in air compared to those of others using a different method are in good agreement. The above stated equations as derived in this paper are presented and the process time for applying the new method has been greatly improved.