In order to solve the problem of poor microhole quality in millisecond/nanosecond laser processing, the 515 nm picosecond laser was used to ring cutting stainless steel with a thickness of 0.1 mm to process microholes with a diameter of 100 μm. Laser confocal microscopy was used to observe and characterize the morphology and quality of the processed microstructure. The effects of laser energy density, scanning speed and defocusing amount on the morphology and quality of microholes after processing were studied. The experimental results show that the energy density has a direct influence on the inner wall quality of the microholes. Controlling the energy density below 6.45 J/cm2 can effectively reduce the heat affected zone of the inner wall of the microholes under the premise of ensuring the removal ability. At the same time, it is found that appropriately increasing the scanning speed can improve the quality of the microhole incision and the inner wall of the ring cutting. When the laser energy density is 6.45 J/cm2 and the scanning speed is 200 mm/s, the hole taper is 2.72 degrees. As the scanning speed increases, the taper decreases, and finally stabilizes at about 2.29 degrees. The taper of the hole can also be reduced to some extent by the positive defocusing process. The results of this study show that the optimized process parameters can process microholes with small heat affected zone, good edge quality and small taper.