Nowadays, diabetes is a serious problem that threat people's health. Hence diabetes management becomes increasingly important. However, blood glucose detection, as an important part of diabetes management, is still a challenge due to the invasion and inaccuracy of non-invasive methods. In this research, we developed our custom-made spectrum domain optical coherence tomography (SD-OCT) system for non-invasive blood glucose detection. We used the laser with center wavelength of 980nm where the absorption of glucose and water are both low, which is suitable to OCT imaging. By applying a dispersing prism, higher solution spectrum could be obtained to acquire better OCT images and more accurate glucose concentration. And the light path with free-space construction was applied for easily constructing, analyzing and controlling the light in the system. Additionally, light with wavelength of 980nm, partly limited by optic fiber construction, could be applied better in free-space construction. We have built a free-space spectrum domain OCT system whose tomography function has been proved by scanning onion sample. Furthermore, pristella maxillaris was used as sample to study glucose monitoring. Pristella maxillaris is a kind of fish with transparent body structure and suitable size, and thus we considered to be an ideal animal for the blood glucose measurement by optical methods. In the experiment, five groups of fish cultivated in glucose solutions with different concentration. The OCT signals of the five groups of experiments arrayed up to down as the glucose concentration rising, which conformed to the theory and proved our method of its potential in measuring blood glucose concentration non-invasively.