The present invention belongs to the field of digital signal processing technology and features that the strength difference between the target signal and the background signal is used in back estimation by means of coordinate conversion. The process includes the first polar coordinate conversion according to the strength difference between the target signal and the background signal, the subsequent calculating the convex hull of the converted signal and the inverse conversion of the vertex of the convex hull in the polar coordinate to obtain backgrounds on signal in rectangular coordinate system, and final interpolation to estimate the signal/background ratio by using the background points as the key interpolation points. The process is simple, high in precision and especially suitable for condition with soft target edge and inhomogeneous background.