Two leaves and a bud of the Jiukeng tea variety were selected as the raw material to conduct trial production of green tea. Three different first-firing degrees, namely heavy, moderate, and mild, with a leaf water content of 15%, 20%, and 25%, respectively, were achieved through first-firing treatments. The effects of the three levels of first-firing on the biochemical components, the dry tea color parameters, the tea liquor color parameters, and the sensory quality of the tea samples were analyzed to determine the appropriate water content degree of first-firing green tea processing. The results showed that with a high first-firing degree, the total flavonoid glycosides, appearance greenness (Sa), and liquor greenness (La) were significantly high (p<0.05), whereas the sweetness value and the Sb/Sa or yellowness to greenness ratio for appearance, was significantly low (p<0.05). Furthermore, compared with mild first-firing, under heavy first-firing, the sweetness value and Sb/Sa value decreased by 38.53% and 78.88%, respectively, and the values of Sa, La, and total flavonoids increased by 47.11%, 11.02%, and 3.17%, respectively. Moderate first-firing treatment (20% moisture content) also led to relatively high amino acid, glucose, sweetness value, the ratio of yellowness to greenness (Lb/La) of the liquor, and relatively low phenol-ammonia ratio, total catechin, andtotal flavonoid glycosides providing the material basis for high-quality green tea. This treatment resulted in improved light green and bright color, tender aroma, fresh and mellow taste quality of the green tea, and a total sensory score (92.2) of 1.25 and 2.25 points higher than those of heavy and mild first-firing treatments, respectively. In addition, the Lb/La value of moderate first-firing was significantly higher than that of heavy and mild first-firing green tea by 3.14% and 4.25%, respectively (p<0.05). PLS-DA results showed that Lb/La, brightness of liquor color (LL), ester catechins, kaempferol-3-O-rutin glycoside, and phenol-ammonia ratio were the distinctive characteristic components of green tea under different first-firing degree conditions, and can serve as the control indexes for the drying process of green tea. In conclusion, a leaf moisture content of 20% could serve as the standard of moderate first-firing.