The invention relates to the field of welding in the equipment manufacturing industry, in particular to a welding process of a high-precision optical instrument base frame. The welding process is suitable for welding of the high-precision optical instrument base frame of a 304 stainless steel material. Manual arc welding is adopted for welding the 304 stainless steel base frame. The type of an adopted 304 stainless steel welding electrode is E308-15, the welding electrode diameter is phi4.0 mm, and the power polarity is direct current reverse polarity. The welding process comprises the steps of pre-welding treatment, the welding process and postwelding heat treatment. According to process parameters in the welding process, the welding current ranges from 250 A to 280 A, the welding voltage ranges from 28 V to 32 V, and the welding speed ranges from 280 mm/min to 320 mm/min. According to the welding process, the problems about assembly locating precision, welding deformation, welding efficiency, weld bead quality and the like are solved, and the weld strength is guaranteed by selecting manual arc welding materials, wherein chemical components of the manual arc welding materials are similar to those of the materials for frame welding, and the strength of the manual arc welding materials is matched with that of the materials for frame welding. The welding deformation is effectively controlled through the assembly welding sequence.