Boundary condition is an important issue in acoustic calculations, and free acoustic field is often simulated by non-reflection boundary in acoustic calculations. At present, the main simulation methods are radiation boundary method, characteristic acoustic impedance method and PML method in non-reflection boundary. Acoustic numerical calculations of non-reflection boundary were studied, the theoretical basis of three non-reflective boundaries was summarized. With plan wave incidence of free field for example, the acoustic absorption capacity and application of three kinds of boundary were analyzed and summarized. For the question of large incidence angle, PML method has the best non-reflective ability, radiation boundary method and characteristic acoustic impedance method will produce a greater error.