The present invention relates to an optical module and system for a liquid sample, and more particularly to an optical module and system for measuring a property of a liquid sample. The optical system comprises a substrate, a laser source, at least one photo detector, and a microprocessor, wherein the substrate comprises a sample surface at the top, a light-out surface, and an extruded light guide block with a light-in surface at the bottom. The extruded light guide block guides light from the light-in surface to the sample surface with a useful incident angle. In the present invention, the analysis can be processed with the normalized intensities of the reflected and scattered light for enhancing the accuracy of the system.