To a RSS visible light positioning system based on an amplifier with fixed gain, the detectable range of the light intensity is small, which leads to very low positioning accuracy in the area with weak signal and then results in a decreased space of effective positioning. A RSS visible light positioning system based on an amplifier with dynamically adjustable gain is proposed, where the gain of the main amplifier is adjusted automatically in light of the feedback from the output of the signal processor, thus the detectable range of the light intensity is extended, the positioning accuracy in the weak signal area is improved and the effective positioning space is expanded. Experiments show that within experimental space of 1 m×1 m×1.89 m, the positioning with high precision can be reached in 1.0 m×1.0 m×0.6 m space range, where the effective positioning space is expanded approximately 86.72% in comparison to a fixed gain positioning system. Experiments in a two dimensional plane indicate that in the coverage with low signal intensity, the average positioning error is decreased 47.05% for the dynamic gain system compared with the fixed gain system. The average system error is lowered to be less than 5 cm. The study leads to the conclusion that the positioning space is expanded effectively and the positioning accuracy in the weak light signal region is enhanced while the predefined high accuracy requirement of positioning is promised.