Laser induced fluorescence (LIF) technique can measure concentration field without disturbing flow, and make for studying the mixing characteristics, but many factors would affect fluorescence in the experiment, analyzed all factors and got relation between concentration and fluorescence intensity. Experiments found sheet light energy was not uniformity, so measurement region was divided into three parts: left region, middle region and right region through the distribution of fluorescence intensity. Applied calibration experiment, linearity of concentration versus fluorescence was attained in every region. In elliptic jet experiments, calibration curve was applied to study mixing characteristics, including gauss distribution and centerline concatenation decay at major axis plane.