In the melt direct spinning polyester staple fiber production line, 1.33 dtex polyester staple fiber modified by graphene was produced by blending modification subsequent to adding graphene masterbatch to polyester melt through an on-line addition device. The effects of process conditions such as drying temperature, the addition amount of graphene masterbatch, and the spinning temperature, drawing, setting on fiber forming and product quality were investigated. Under the conditions of masterbatch drying temperature of 150 ℃, the 0.5% mass fraction of masterbatch added, spinning temperature of 288 ℃, ring blowing wind speed of 1.15 m/s, draw ratio of 3.58 times, and tension heat setting steam pressure of 0.8, 1.2, 1.8, 1.8 MPa, the titer of the graphene modified polyester staple fiber is 1.32 dtex. The breaking strength is 5.92 cN/dtex, the elongation at break is 23.8%, the defect content is 0.5 mg/100 g, the dry heat shrinkage rate at 180 ℃ is 6.2%, and the spinning and drawing production is in good condition. The performance indexes of fiber meet the requirements.