A system and method for detecting the recognizability of input speech signal is provided. It is designed in the pre-stage of speech recognition or a dialog system. The invention detects the user's environmental condition and verifies if the input speech signal can be recognized. It mainly comprises an environment parameter generator, a signal recognition verifier, and a strategy response processor. Through the use of the invention in the pre-stage of speech recognition or a dialog system, it can precisely verify the recognizability of the input speech signal and receives the input speech signals of high recognition probability in a noisy environment. This reduces the impact caused by receiving the input speech signals of low recognition probability. This invention thus increases the recognition probability for a recognizer.