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Doppler ultrasound instruments, used for the detection and monitoring of vascular disease, require a means of separating the large, low frequency Doppler signal from the vessel wall from the signal arising from blood followed by a means of analysing the blood flow signal in order to characterise the flow conditions. This is normally achieved by using a high-pass filter that removes the signal reflected from the vessel wall. Unfortunately, the filter also removes the low frequency Doppler signals arising from slow moving blood. A better signal segmentation method that reduces the loss of signal from slowly moving blood is needed to permit the measurement of lower blood velocities. A signal simulator that generates Doppler signals that include the contributions from blood and vessel wall will be very useful for the development of new Doppler signal segmentation methods. This work presents a new simulator incorporating the contribution of blood and vessel wall movements; the characteristics of the simulator output signal are similar to those found in practice.