The invention belongs to the field of mechanical equipment detection and application, and relates to a rapid modular numerical control lathe machining precision detection device and a detection method. The detection device comprises a framework module, a line laser detection module and an optical fiber probe detection module. The line laser detection module comprises a line laser transmitting end,a line laser receiving end and an inner gear ring. The optical fiber probe detection module comprises a circuit board shell, a roughness optical fiber probe, a distance measuring laser probe and a metal contact pin. The circuit board shell, the roughness optical fiber probe and a fixing support column are integrated. The distance measuring laser probe and the metal contact pin are integrated. Thedetection method of the detection device comprises the steps that the line laser detection module is arranged for detecting roundness and radial run-out of a workpiece; and the optical fiber probe detection module is used for detecting the surface roughness, axial run-out and turned end face precision of the workpiece. According to the rapid modular numerical control lathe machining precision detection device and the detection method, on the premise that the clamping relation of the workpiece is not changed, the shape error, the rotation error, the surface roughness and the turned end face precision of the machined workpiece are detected online in real time, and convenience and rapidness are achieved.