A conjugate gradient full waveform inversion program is coded to verify the effectiveness of full seismic waveform inversion and to study its characteristics. Firstly, a one dimensional inhomogeneous model is inverted using one source and one receiver. Then, by modifying different parameters of the inversion, the factors that affect the inversion result are discussed. It is shown that full waveform inversion can produce accurate result when data is abundant. The number of sources and stations is the primary factor that affect the inversion result. Multiscale inversion and better initial model can significantly improve the stability of the inversion. Noise applied to the observed seismogram can cause small scale disturbance on the result, though large scale characteristics of the result remain more or less unaffected.