AFVISAR (all fiber velocity interferometer system for any reflector), which is developed from laser Doppler method, has been proved to be effective and powerful technique in acceleration (and velocity) measurement. The measuring error of AFVISAR system must be studies in order to achieve accurate measure result. However, the existing theoretical research about this problem is inadequate.In this paper, firstly, the principle of AFVISAR is analyzed with Doppler frequency shift theory and the mathematic equations for acceleration calculating are concluded. The theoretical model of the measuring error is put forward by considering object moving direction bias angle and corresponding expression of the deviation is established. Then, an example is taken to illustrate the effect that the bias angle brings to acceleration calculation. In the following paragraph, the error creating by ignoring the second-order Doppler frequency shift is analyzed and the calculation formulas are demonstrated. Finally, the effect of the spectral characteristics of fiber laser are studied, and the relative error is calculated.