Aiming at the influence of the 12 bit quantization error on the four-parameter sinusoidal fittingaccuracy, the fitting error bounds were researched among the five parameters of effective bits, amplitude, frequency, initial phase and DC component. The selected condition variables are amplitude, the number of cycles of the waveform contained in the sequence, the initial phase, the DC component and the number of sequence data points. The error boundary search was carried out in a two-condition combination styles, and the error curves of the above five parameters were gained under each condition, including both the upper and the lower error bounds. The results can be used to estimate the error and uncertainty of the fitting parameters, or to construct the measurement conditions under the sitting fitting error and uncertainty.