The prefabricated keyhole effects on the radiation characteristic of laser-induced stainless steel plasma were investigated. A high-energy neodymium glass pulse laser was used to ablate stainless steel sample in air at atmospheric pressure. Combined-type multi-function grating spectroscope and CCD spectral acquainting and processing system were used to record plasma spectrum. The electron temperature and the full width at half maximum of spectral line, respectively. The study results showed that the spectral intensity and signal-to-background ratio of laser plasma increase in the range of 71.5%～125.8% and 7.6%~18.5% respectively when a laser beam (～5 J) acted on the stainless steel sample on which prefabricated keyholes (d=1.5 mm, h=0.8 mm) were placed. The plasma temperature and electron density increased by about 1 200 K and 1.21×1016 cm-3, respectively. This proved that prefabricated keyhole had a significant enhancement effect on the radiation of laser-induced stainless steel plasma.