Abstract: 【Objective】 This study aimed to observe the performance of substrates of different peat particle sizes and cultivation effects， investigate the driving mechanisms of peat particle size ratios for regulating substrate water suction characteristics， and screen the optimal substrate formulas with optimal performance， providing scientific reference for high-quality horticultural substrate formulas. 【Method】 A total of 18 blended substrate treatments were formulated using peat of different particle sizes （D_{3-5 mm}， D_{1-3 mm}， and D_{0.5-1 mm}） combined with two inorganic materials （vermiculite and fly ash） to determine substrate physicochemical properties， water suction， nutrient preserving capacity， and pakchoi cultivation effects of different treatments. Redundancy analysis was used to investigate associations between substrate performance and cultivation effects. 【Result】 Different peat particle size ratios and inorganic materials markedly influenced substrate physicochemical properties， water suction， and nutrient preserving capacity. Under the same peat particle size ratio， compared to blended vermiculite substrate， blended fly ash substrate showed an average increase of 39.16% for bulk density， an average decrease of 27.62% for aeration porosity， an average increase of 11.60% for water-holding porosity， an average decrease of 35.36% for air-water ratio， an average increase of 153.93% for electricity conductivity， an average decrease of 23.87% for alkaline hydrolyzable nitrogen content， an average decrease of 32.08% for available phosphorus content， and an average decrease of 11.66% for ammonium nitrogen content. Kostiakov model could simulate the substrate water suction characteristics fitting efficiency （R²） was 0.963-1.000， root mean square error （RMSE） was 0.300-3.694， and the parameter b clearly distinguished the water suction intensity， with b ranging from 0.87 to 2.22 across treatments. The nitrogen fertilizer lost in different blended substrates was mainly nitrate nitrogen. The cultivation effects were jointly influenced by water suction and nutrient contents of blended substrates. When the ratio of small peat particles （D_{0.5-1 mm}） in the substrate was 60%， the blended substrates exhibited the strongest water suction and nutrient preserving capacity， showing the optimal pakchoi cultivation effects. Redundancy analysis showed that the Kostiakov model para-meter a， water-holding porosity， and nutrients in the substrate exhibited positive effects on cultivation effects， while the Kostiakov parameter b， substrate aeration porosity， air-water ratio， electrical conductivity， and bulk density exhibited negative effects on cultivation effects， indicating that cultivation effects were synergistically influenced by physical properties and nutrient indicators. 【Conclusion】 The blended substrate performance is commonly controlled by peat particle size ratios and inorganic materials. To enhance water suction and nutrient preserving capacity， peat dominated by small particles and fly ash are recommended to formulate substrates.