A high resolution hybrid linear ion trap time of flight mass spectrometer（LIT-TOF MS） was constructed，which is based on the time of flight mass spectrometry，linear ion trap，atmospheric pressure ionization source and other core technologies.The performance of the instrument was characterized with an electric spraying ion source.The resolution of LIT-TOF MS was over 12 000（Reserpine，m/z 609），the mass range was 33-1 922 amu，and the sensitivity was 1 μg/L.It was also demonstrated that MS3 could be readily performed in the LIT.The qualitative and quantitative analyses on amino acids were carried out by the LIT-TOF MS，and results showed that it could be used in the real time，on line and high throughput determination of contents and variations of amino acids in biological complex samples.Besides，the instrument，combined with a variety of atmospheric pressure ionization techniques，could be applicable for determination in fields of medicine，environment and foods，etc.