The invention provides a three-coordinate measuring method of a tenon tooth blade, which solves the problems of unstable measuring data and the like caused by unfit point taking positions of measuring points when digital to analog fitting of three-coordinate measuring is carried out by a traditional tenon tooth blade. The three-coordinate measuring method comprises the following steps of, firstly, supplying a visual blade to a three-coordinate measuring procedure with the utilization of a UG (Unigraphics), wherein a measuring coordinate system and a visual blade coordinate system are automatically superposed by a three-coordinate measuring system; secondly, coarsely establishing a reference; thirdly, carrying out digital to analog fitting; and fourthly, checking the coincidence degree of the visual measuring coordinate system and the blade coordinate system after digital to analog fitting, repeating the digital to analog fitting process if the coincidence degree does not meet the requirements, and measuring and evaluating the blade if so. The three-coordinate measuring method is characterized in that iterative error radius is 0.03mm when the reference is coarsely established; the working surface of a first grain tooth of an inner-back arc at the root of the tenon tooth blade is uniformly divided into three parts, and two points are taken from each part; the working surface of a second grain tooth of the inner-back arc at the root is uniformly divided into three parts, and one point is taken from each part; and six points are taken from the locating side surface of a blade root, and a point is respectively taken from tooth depth of the first grain teeth of the inner arc and the back arc of the root near the steam inlet side surface and the air outlet side surface.