The present invention provides a plant growth system and an optical radiation control method of light source for plant growth. The plant culture system includes a container with at least one plant grows therein, arranged in a growing space a light source for plant growth arranged above the container by a light intensity adjusting apparatus a sensor and a processer, wherein the sensor arranges in the growing space and electrically connects to the processer, and wherein the processer further electrically connects to the light intensity adjusting apparatus. Specially, the sensor is configured to detect the vertical distance between the light source and an upper leaf of the plant, and the processer is configured to control the light intensity adjusting apparatus to change the light projection angle of the light source.本發明揭示一種植物栽培系統及植物生長光源之強度控制方法。植物栽培系統包括:栽種有至少一植株的一栽培容器,配置於一培育空間內;一栽培用光源,藉由一光強度調整裝置配置於植株上方;一感測器及一處理器,感測器同樣配置於培育空間內並電性連接處理器,而處理器進一步電性連接光強度調整裝置。本發明的植物栽培系統於運作時,感測器能偵測栽培用光源與植株的上位葉之間的垂直距離,處理器能根據垂直距離來控制光強度調整裝置,以調整栽培用光源的光投射角度。S‧‧‧植物培育系統1‧‧‧箱體11‧‧‧培育空間2‧‧‧栽培容器3‧‧‧光強度調整裝置31‧‧‧角度調整機構311‧‧‧固定基架312‧‧‧旋轉基座313‧‧‧移動升降組件32‧‧‧動力機構33a‧‧‧感測器4‧‧‧栽培用光源5‧‧‧環境調節模組C‧‧‧垂直軸線H‧‧‧垂直距離
