This paper introduces a fiber optical spectrograph which can directly measure the liquid of the living body. Based on the property of fiber optical and capillary, the authors design a special optical fiber probe which can directly insert the living body to sample the liquid and plunge the liquid into the optical path. That is ,the sample liquid can be directly tested without any pre processing. So this operation simplified the detecting process and perform measurement in situ. In order to improve the sentivity of the probe, the optical fibers in the probe are distributed in layers so as to increasing the optical length of the living liquid. On the other hand, the computer control the stepward motor to rotate through the pulses emitting from the parallel port of the computer so as to drive the quart prism rotating. The optical signal is accepted by the photomultipler and sampled by the computer. This spectrograph can display in time the spectrum of the living liquid on the screen. Through analysing the spectrum of the living liquid, many living parameters can be detected.