Abstract: Digitally reconstructed radiograph(DRR) has been widely used in computer assisted diagnostics and 2D-3D medical image registration applications.This paper designs a new projection model that can release the interconnection of image scale and projection distortion.Therefore,this model can create projection image with a higher accuracy in image scale.Based on this model,an improved RayCasting method,which employs the image region homogeneity to accelerate the integration process along the X-ray beam,is proposed.According to the experimental result,this method is faster than the traditional RayCasting method when it comes to the data with high homogeneity.This method can preserve the accuracy of the object edges.