Abstract: In order to promote the content and quality of γ-aminobutyric acid (GABA) in γ-aminobutyric acid-rich yogurt, defatted reconstituted dairy was taken as the main raw material, Lactococcus lactis subsp. lactis with high-yielding potential of GABA in dairy-based medium selected previously by research group was used as start culture, viable count, yield of GABA, residue of L-Glu-Na and sensory evaluation were taken as evaluation indexes, to carry out research on optimizing the fermentation process of yogurt rich in GABA. Through single factor experiment and uniform experiment, model equation of double-strain mixed fermentation in defatted reconstituted milk was derived, and the optimal fermentation conditions were determined. Results showed that: Compound strain was Lactobacillus casei, proportion of Lactococcus lactis subsp. lactis and Lactobacillus casei 1:3, fermentation time 48 h, fermentation temperature 32 ℃, addition of L-Glu-Na 8 g/L. Finally, the yield of GABA was 4.10±0.10 g/L, which was 3.78 times of that before optimization. In addition, viable count was 3.03×10¹⁰±1.75×10¹⁰ CFU/g, acidity of yogurt was 129.67±2.08 °T, residue of L-Glu-Na was 0.11±0.01 g/L, all indexes met the requirements of GB19302-2010 National Food Safety Standard Fermented Milk, and the sensory evaluation score was 78.42±4.63. This process would be hopeful to provide a basis for development of more fermented dairy products rich in GABA.