Based on the fundamental principles of velocity measuring in the frequeucy domain，a trajectory FFT spectrum analyzer is studied. First of a11，the construction of the system is given. Then，some basic algorithms，which can improve the frequency precision，resolution and dynamic range under the circumstance of strong clutter interference are studied. The paper a1so put emphasis on the design of a programmable A/D data acquisition system and a high speed FFT co-operation system which is based on TMS32010.An IBM/PC microcomputer，the weighted ZFFT analyzing software and the above two systems form the whole frequency spectrum analyzing system.