An adjustable prosthetic leg, adapted to be connected between a thigh and an artificial foot, comprising: a controller provided with a first pivoting portion and a second pivoting portion, wherein said controller is adapted to be connected to the thigh; a hydraulic unit provided with a third pivoting portion, a hydraulic cylinder, a reserve hydraulic cylinder, a brake hydraulic cylinder, an adjust-initiating compartment comprising an elastic element, and a flow system, wherein said hydraulic unit is pivotally connected to said controller so that said hydraulic unit pivots directly about said second pivoting portion, and said hydraulic cylinder, said reserve hydraulic cylinder, and said brake hydraulic cylinder are in communication with each other through said flow system, said flow system having first and second flow paths (351, 352) in communication with both a lower hydraulic compartment of said hydraulic cylinder and said reserve hydraulic cylinder, said first flow path being in communication with said lower hydraulic compartment and said reserve hydraulic cylinder via said brake hydraulic cylinder, and said second flow path bypassing said brake hydraulic cylinder; a connecting mechanism that is pivotally connected to said controller so that said connecting mechanism pivots directly about said first pivoting portion, and said connecting mechanism extends into said hydraulic cylinder of said hydraulic unit; and a shell that is pivotally connected to said third pivoting portion and presses against the elastic element in said adjust-initiating compartment, wherein a horizontal angle formed between said second pivoting portion and said third pivoting portion is 40 to 60 degrees, and said shell is further connected to said artificial foot. a controller provided with a first pivoting portion and a second pivoting portion, wherein said controller is adapted to be connected to the thigh; a hydraulic unit provided with a third pivoting portion, a hydraulic cylinder, a reserve hydraulic cylinder, a brake hydraulic cylinder, an adjust-initiating compartment comprising an elastic element, and a flow system, wherein said hydraulic unit is pivotally connected to said controller so that said hydraulic unit pivots directly about said second pivoting portion, and said hydraulic cylinder, said reserve hydraulic cylinder, and said brake hydraulic cylinder are in communication with each other through said flow system, said flow system having first and second flow paths (351, 352) in communication with both a lower hydraulic compartment of said hydraulic cylinder and said reserve hydraulic cylinder, said first flow path being in communication with said lower hydraulic compartment and said reserve hydraulic cylinder via said brake hydraulic cylinder, and said second flow path bypassing said brake hydraulic cylinder; a connecting mechanism that is pivotally connected to said controller so that said connecting mechanism pivots directly about said first pivoting portion, and said connecting mechanism extends into said hydraulic cylinder of said hydraulic unit; and a shell that is pivotally connected to said third pivoting portion and presses against the elastic element in said adjust-initiating compartment, wherein a horizontal angle formed between said second pivoting portion and said third pivoting portion is 40 to 60 degrees, and said shell is further connected to said artificial foot.