The invention relates to an optical system and method for liver function test. It comprises an infrared laser module, a received module, and an output module. The present invention uses a fluorescent receiver collocating with an infrared laser beam with 785 nm wavelength for detecting a fluorescence reaction of an indocyanine green (ICG) dye to produce a continuous data chart about ICG reaction with time. It can be applied to the purposes of a health examination for hepatic circulation function test and a clinical liver surgery for continuous ICG detection of the cells on the hepatic surface to effectively reduce data errors due to that the ICG testing time can not be controlled accurately to enhance the accuracy of a liver function test and a clinical surgery detection positively.
