A rapid detecting instrument of bacteria was presented based on the principle of Adenosine Triphosphate(ATP) bioluminescence.In the instrument, a high-precision A/D converter and a small Photomultiplier Tube (PMT) module were included to improve the optical detection sensitivity, and the optical, circuit and software designs were integrated to construct the rapid detecting system for bacteria combinated with homemade ATP bioluminescence biosensors.Standard bacterium suspensions were detected to study the relation of Relative Light Units (RLU) and the concentration of bacteria, and the Correlation Coefficient (R) is 0.976 0.In order to detect actual samples, an improved data processing algorithm was bring forward, and modified modulus were imported in the equation.Furthermore,the detecting concentration of bacteria in a hericium erinaceus sample was demonstrated by the proposed system, results show that the R is 0.993 compared with the result obtained by the standard Aerobic Plate Count (APC) method.The reproducibility of the system was tested and its Relative Average Deviation (R.A.D.) is 7.69 % and Coefficient of Variability (CV) is 9.07 %.The BCG vaccines were also detected by this system and the R is 0.997 compared with the result obtained by the APC method.its R.A.D.is 7.69 % and CV is 9.07 %.It is concluded that this system can complete the process of detection in few minutes, and can offer its high sensitivity and reproducibility.