Based upon the binary collision approximation (BCA), the Monte Carlo methods are employed to study sputtering of multi-component amorphous targets. Total and partial sputtering yields, energy and angular distribution and the escape depth distribution of sputtered particles are given. The changes of surface concentrations are also studied The results indicate that the collisional effect may account for the preferential sputtering, which plays an important role in surface composition changes due to ion bombardment.