Abstract: A method of auto scanning and scraping a work piece for a hard rail has a preparing step, a scanning step, a detecting step, an auto-scraping step and an analyzing step. The preparing step comprises preparing an auto scanning and scraping apparatus with a multi-axis machine tool, a control computer, an auto-scraping device and a position detector. The scanning step comprises scanning the surface of the work piece to read the roughness value and transporting the data to the control computer. The detecting step comprises forming a 3D-appearance drawing of the work piece and detecting the 3D-appearance drawing with multiple detection steps. The auto-scraping step comprises scraping the surface of the work piece by the auto-scraping device. The analyzing step comprises detecting the 3D-appearance drawing of the work piece that has been scraped with the preceding detection steps and scraping the work piece to meet the preceding detection steps.