Based on laser induced fluorescence detection a miniaturized and sensitive optical system is developed for micro total analysis systems (u-TAS) application. A micro optical system integrated with a micro fluid device is a convenient way to realized biochemical reaction and detection on one chip. Such a bi-functional micro system for DNA affinity assay is presented in this paper. The optical system composed of optical fiber coupling with planar waveguide for illuminating the labeled DNA samples, and micro lens arrays for collecting the induced fluorescence light. High signal-to-noise ratio can be achieved because of evanescent field excitation mode. A specially designed micro chamber, with chemical process, including small pipes for guiding sample agent is included in the system in order to enable DNA affinity reaction, and to wash the chamber afer reaction. These components will be integrated within the encapsulation of a photoelectric array detector, so the size of this system can be greatly reduced. This bi-functional micro system has merits of integration of reaction and detection together, more compactness, multi-channel detection, high sensitivity and good compatibility with biological samples. This system is a promising candidate to be integrated into a micro total analysis system, such as a portable DNA diagnostics device.