The invention discloses a pre-treatment method for detecting heavy metal sewage by means of laser induced breakdown spectrometry. The method is characterized by comprising the following steps: adjusting the power of hydrogen of the sewage; adding a nano oxide into the heavy metal sewage in proportion for adsorption; uniformly mixing the mixture and separating and drying the same; and tabletting the prepared powder for detection. The sample pre-treatment method of adsorbing heavy metal ions of sewage by means of the nano oxide provided by the invention solves the problems that the liquid splashes, the service life of plasma is short, the signal intensity is low and the like in a direct detection process by means of laser induced breakdown spectrometry for liquid samples such as sewage. The method provides simple and effective feasibility for iron enrichment, and the sensitivity and detection limit of the spectrum detection method are effectively improved.