To improve the reliability and security of maching exact details in space equipment and to shorten their developing periods,a real-time detecting method for the metal cracks in machining exact details was presented. According to this method, a prototype machine of real-time detecting instrument for the cracks of exact details based on a float digital signal processor—TMS320F28335 was developed. In consideration of online real-time detecting, the Acoustic Emission(AE) technique was adopted in the method. The general scheme for detecting metal cracks in real time was introduced and the hardware composition and software algorithm corresponding to the system were analyzed in detail. Finally, the verification experiments to the prototype machine of real-time detecting instrument were carried out. The experimental results show that the prototype machine has high performance. Its false detecting ratio reaches 1.2% and has no missing cracks,which validates that the AE real-time detec-ting method for the crack detecting is efficiency.