Based on the theory proposed by Walls et al, an experimental scheme of quantum non demolition (QND) measurement for intensity difference fluctuations is put forward, which is realized though a nondegenerate optical parametric amplifier. The relations of transference coefficients and the ability for quantum state preparation are deduced on the nonideal condition, and the influences of probe input noise spectrum and measurement efficiency of detection system on the measurement criteria are discussed, respectively. In conclusion, the smaller probe input noise and the larger measurement efficiency, the measurement quality is better and more sensitive to the measurement efficiency.