Abstract: This paper presents a new modeling method of microwave VCO( Voltage Control Oscillator). Based on this model a novel board bandwidth microwave noise generator , which is composed of a digital algorithm part and an analog modulation part, is simulated. This noise generator features broad adjustable bandwidth( from 30MHz to 300MHz) and wide central frequency range( from 8GHz to 18GHz). The comparison of simulative with experimental results of the generator is give. And the causes of agreements and disagreements are also analyzed. The accordance between simulative and experimental results, such as 3dB band-width and in-band flattness, indicates the validity of the presented modeling method.