Alpha-decay propulsion technology, a microthrust technology based on thin spontaneous-alpha-decay films, is proposed in this paper. A large quantity of decayed alpha particles emitted from the upper surface of thin films would generate thrust statistically. Simulations were executed using the Monte Carlo N-Particle Transport Code (MCNP) to acquire the energy and angular distributions of escaping alpha particles, as well as the key parameters of alpha-decay films. A 22.40-μm 210Po film combined with a 20-μm aluminum film was able to generate an average thrust of 29.5 nN/cm2 in half-life time. The remaining charges and thermal energies of the decay films were considered. Directional-generated alpha particles were simulated to analyze the influence of angular scattering on escaped alpha-particle distributions. Alpha particles with low energy, with large scattering angles, or with large generated angles contributed less to thrust value. With the assumptions of no scattering, constant stopping power, and no range struggling, a set of analytic formulas were derived. Comparisons of the distributions and typical parameters between simulations and the analytic model were conducted. Discrepancies were mostly caused by the three assumptions and were less than 3.7% for thrust and less than 3.9% for the proportion of escaped alpha-particles.