Recently, near-field scanning optical microscopy (NSOM) and its variations, which combine the scanning probe technology with optical microscopy, have been intensively applied in the study of biology, material science, surface chemistry, information storage, and nanofabrication. However, due to the serial scanning nature, the speed at which NSOM can successively records highly resolved images is rather limited. This hampers the applications of NSOM in characterizing dynamic response of particular samples. In this article, we perform systematic investigation of NSOM system parameters, which include scan rate, signal detector amplification, and illumination intensity. In this work, a model of signal flow for the NSOM system has been established to quantitatively investigate the interplay of the key process parameters and to further explore the technique solutions for high-speed NSOM imaging. The model is in good agreement with experimental results and the optimized conditions for high speed NSOM imaging are suggested.