The invention relates to a ground terrain automatic profiling system suitable for an agricultural machine. The system comprises a profiling head basic part, a profiling touch plate, an ejector rod, a swing frame, an angle sensor, an electric control system and a profiling lifting oil cylinder. One end of the profiling touch plate is hinged to the profiling head basic part and suspended at the lower end of the profiling head basic part, the middle of the profiling touch plate is hinged to the lower end of the ejector rod, the upper end of the ejector rod is connected with the free end of the swing frame through a pre-pressing buffering spring, the other end of the swing frame is connected with the angle sensor, the angle sensor converts an angle change range of the angle sensor into a voltage or current signal, the voltage or current signal is transmitted to the electric control system, and a processing result is output to the profiling lifting oil cylinder through analysis and processing of the electric system. By means of the ground terrain automatic profiling system, a work mechanism can adapt to terrain changes, and the stability and reliability of the machine are improved.