Hemodynamic parameters of the pulmonary circulation are important reference factors in the diagnoses and treatments of children?s cardiovascular diseases. These parameters are usually measured by the cardiac catheterization. Recently several noninvasive methods have been proposed to estimate these parameters using the ultrasound technique. In order to execute the noninvasive estimation automatically, several signal and image processing algorithms are applied to obtain the feature points of the Doppler spectrogram and ECG signal, from which hemodynamic parameters can be calculated based on empirical formulas. To combine all the processes and simplify the manipulation, a computer-based system is designed and tested for sixty children with congenital heart diseases. Experimental results show that parameters estimated using this system highly correlate to the clinic ones measured by the cardiac catheterization. For its noninvasive and automatic advantage, this system may be used as an assistant tool in the diagnoses and treatments of children?s cardiovascular diseases.