In the present invention, a voice input system and a voice input method are provided. The voice input method includes the steps of: (A) initiating a speech recognition process by a first input associated with a first parameter of a first speech recognition subject; (B) providing a voice and a searching space constructed by a speech recognition model associated with the first speech recognition subject; (C) obtaining a sub-searching space from the searching space based on the first parameter; (D) searching at least one candidate item associated with the voice from the sub-searching space; and (E) showing the at least one candidate item.