The present disclosure utilizes the MEMS (Micro Electro Mechanical Systems) process and packaging method to produce a microsystem for analyzing blood which is capable of detecting several kinds of ions. The microsystem for analyzing blood has a miniaturized reference electrode, so size of the microsystem can be greatly reduced. The microsystem further has a gate detecting area larger than a conventional planar ISE or a conventional ISFET does, so interference with signals can be avoided, and packaging difficulty and blood leakage can be reduced. Therefore, the microsystem is thin and small, reacts rapidly, and has a high accuracy, and a high compatibility with IC (integrated circuit) process. In addition, the microsystem has high stability of long-term potential, low offset-potential characteristics, low alternating current impedance, high stability of dynamic reference potential, low electrochemical noises and high reproducibility of the electrode.