Abstract: To address the problems of serious soil acidification, nutrient imbalance and decline of tea production and quality in the perennial tea gardens, a field experiment was conducted in a seven-year-old acidified tea garden to explore the effect and mechanism of biochar based fertilizer on soil fertility, the nutrient uptake, yield and quality of tea. Six treatments were set up as follows: control (CK), chemical fertilizer (F), biochar (B), low, medium and high application rates of biochar based fertilizer (BF1, BF2 and BF3, respectively). The results showed that the pH value and the contents of ammonium, nitrogen (NH₄⁺-N), nitrate N (NO₃⁻-N), available phosphorus (P) and potassium (K), exchangeable calcium (Ca) and magnesium (Mg) in the acidified tea garden soil were significantly increased in BF1, BF2 and BF3 treatments compared with CK treatment, and were increased with the application rates of biochar based fertilizer. The improvement effects soil fertility in the BF1, BF2 and BF3 treatments were much better than those in the B and F treatments. The nutrient accumulation, SPAD value, yield and quality, water extract, caffeine and amino acid contents of tea leaves in the BF1, BF2 and BF3 treatments were significantly higher than those in the CK treatment.The phenol-ammonia ratio of tea leaves was significantly lower than that in the CK treatment, and was not significantly different between B and F treatments. The results of grey slope correlation analysis showed that tea yield and quality were closely related to soil pH, the contents of NH₄⁺-N, available K, exchangeable Mg and available P, tea SPAD value, N and Mg accumulation in tea leaves, which were the main factors affecting tea yield and quality. In conclusion, the application of biochar based fertilizer significantly decreased the acidity of acidified tea garden soil, increased the availability of soil nutrients, promoted the absorption of N, K and Mg by tea trees, and enhanced the photosynthesis of tea trees, which led to the significant increase in the yield and quality of tea. The application rate of 2590 kg hm⁻² biochar based fertilizer showed good effect on yield and quality of tea.