The present invention relates to a voice recognition system for replacing a specific domain, a mobile device, and a method thereof, and more particularly, to a technology that divides a search space for voice recognition into a general domain search space and a specific domain search space.A voice recognition system according to an exemplary embodiment of the present invention includes: a mobile terminal receiving a voice recognition target word from a user; and a voice recognition server dividing a search space for voice recognition into a general domain search space and a specific domain search space and storing the spaces, and performing voice recognition for the voice recognition target word through linkage of the general domain search space and the specific domain search space.