The invention discloses an on-line in situ detecting method for an infrared-ultraviolet double pulse laser induced breakdown spectroscopy, which at least comprises the following steps of: A. setting a pulse delay time according to the sample excitation characteristics to control the time interval of two lasers; B. firstly outputting laser from an infrared waveband laser, long-distance collecting, adjusting and focusing on a position to be detected, and ablating the sample to generate plasma; C. outputting laser from an ultraviolet waveband laser after a delay time, long-distance collecting, adjusting and focusing on the same position, and exciting the plasma to reinforce a spectrum signal; D. receiving the spectrum signal through a long-distance spectrum collecting device, coupling the spectrum signal in an optical fiber, transmitting the spectrum signal to a spectrograph, and obtaining the spectrum data information through an assorted software; E. collecting the spectrum data, and obtaining a detection ingredient analysis result by a calibration-free correction analysis method.