An improved scheme of intensity-modulating optical quantization technique for microwave signal is proposed and demonstrated by using double channel sampling. This scheme reduces the complexity and dramatically improves the operation bandwidth by eliminating the need of dual complementary-output intensity modulator. In an experimental demonstration, 8-channel outputs of optical quantization system for microwave signal are obtained with quantization levels of 16. A sinusoidal microwave signal of 2.5 GHz is quantized using pulse sequence with repetition rate of 20 GHz. Good fit sinusoidal curve can be obtained from the quantization values, which proves the feasibility of the proposed scheme.