Abstract: An instrument of on-line analysis the size and chemical composition of single particle with laser bipolar time-of-flight mass spectrometry is described.The inlet system consists of several aerodynamic lenses and chambers which are separated by a nozzle,two skimmers.The aerosol inlet system provides a high transport efficiency for small particles.Using this instrument,we detected the indoor/outdoor aerosols.The technique is excellence in measuring size and inorganic compound.