1. A method for measuring an object, by a first image-capturing device, a second image-capturing device not parallel thereto, and a processing module connected to the first and second image-capturing devices, the method comprising the steps of: (1) capturing a first image and a second image of at least a calibration point of known three-dimensional coordinates by the first image-capturing device and the second image-capturing device, respectively; (2) substituting parameters attributable to the first image and the second image, respectively, and corresponding to the at least a calibration point of known three-dimensional coordinates into a geometric function based on a beam confluence collinear imaging principle, and performing computation on the geometric function with a preset algorithm, so as to calculate a first lens distortion parameter, a first lens center, and a first bearings parameter of the first image-capturing device, and a second lens distortion parameter, a second lens center, and a second bearings parameter of the second image-capturing device, by the processing module, and; (3) substituting the first lens distortion parameter, the first lens center, the first bearings parameter, the second lens distortion parameter, the second lens center, and the second bearings parameter thus calculated into the geometric function based on the beam confluence collinear imaging principle, so as to generate a first beam confluence collinear function and a second beam confluence collinear function which correspond to the first and second image-capturing devices, respectively, by the processing module.