Planar Laser-Induced Fluorescence (PLIF) technique, which is a non-intrusive, fast-response diagnostic method, has been widely used in measurement of various complex flow fields. Both cold flowfield[1-4] and combustion flowfield have made use of PLIF for diagnosis. According to the different flow field and investigation objects, parameters such as fluorescence tracer molecule, laser wavelength, and so forth should be selected seriously in order to obtain the information concerned. This technique was used to investigate complicated flow structure of mixing between transverse jet and supersonic flow, in which acetone and OH radicals were chosen as the fluorescence tracer molecules in the experiments of cold flow and combustion flow respectively. During cold flow measurements, air was used as both the transverse jet and supersonic flow, and liquid acetone was gasfied before adding into the transverse jet, which was excited by laser sheet of 266nm. During combustion flow measurement, ethylene was used as the transverse fuel jet, and combustion between air and ethylene was sustained by plasma discharge. Laser sheet of 283nm was used excite the intermediate product of OH radicals. Fluorescence images were recorded by the intensified CCD camera after filtering interfere light. Both results show that PLIF displays as a credible and valid method for investigating complicated cold flowfield and combustion structure, so long as chosing appropriate fluorescence tracer molecule, laser exciting wavelength, optical filter, et al.