A prosthetic knee joint with buffering and braking effects, the prosthetic knee joint comprising: an upper connecting base having two extending lugs respectively formed on two sides of the upper connecting base and extending backward out of the upper connecting base; and an accommodating recess longitudinally formed through the upper connecting base and disposed between the two extending lugs; a linking assembly pivotally connected to the upper connecting base and having two linking arms respectively disposed on outer sides of the extending lugs, and top ends of the two linking arms respectively and pivotally connected to the upper connecting base; a braking assembly pivotally connected to the two extending lugs of the upper connecting base, disposed next to the linking assembly, and having a braking arm, a top end of the braking arm protruding into the accommodating recess of the upper connecting base and pivotally connected to the two extending lugs; and a lower connecting base connected to the linking assembly and the braking assembly, and having a main body pivotally connected to the two linking arms, and having two connecting protruding lugs formed on a top end of the main body and disposed apart from each other; a receiving recess formed between the two connecting protruding lugs; and a groove disposed in back of the two connecting protruding lugs; the prosthetic knee joint being characterized in that the lower connecting base has an abutment element connected to the main body, being capable of swinging relative to the main body, disposed between the two connecting protruding lugs, pivotally connected to the two linking arms, and having a front end disposed in the receiving recess; a swinging recess formed in a top end of the abutment element, a bottom end of the braking arm disposed in the swinging recess and connected to the abutment element; and a rear end protruding to be disposed above the groove; and a cushion mounted in the groove and abutting a bottom of the abutment element at a position beneath a rotating axis shared by the abutment element and the braking arm. an upper connecting base having two extending lugs respectively formed on two sides of the upper connecting base and extending backward out of the upper connecting base; and an accommodating recess longitudinally formed through the upper connecting base and disposed between the two extending lugs; a linking assembly pivotally connected to the upper connecting base and having two linking arms respectively disposed on outer sides of the extending lugs, and top ends of the two linking arms respectively and pivotally connected to the upper connecting base; a braking assembly pivotally connected to the two extending lugs of the upper connecting base, disposed next to the linking assembly, and having a braking arm, a top end of the braking arm protruding into the accommodating recess of the upper connecting base and pivotally connected to the two extending lugs; and a lower connecting base connected to the linking assembly and the braking assembly, and having a main body pivotally connected to the two linking arms, and having two connecting protruding lugs formed on a top end of the main body and disposed apart from each other; a receiving recess formed between the two connecting protruding lugs; and a groove disposed in back of the two connecting protruding lugs; the prosthetic knee joint being characterized in that the lower connecting base has an abutment element connected to the main body, being capable of swinging relative to the main body, disposed between the two connecting protruding lugs, pivotally connected to the two linking arms, and having a front end disposed in the receiving recess; a swinging recess formed in a top end of the abutment element, a bottom end of the braking arm disposed in the swinging recess and connected to the abutment element; and a rear end protruding to be disposed above the groove; and a cushion mounted in the groove and abutting a bottom of the abutment element at a position beneath a rotating axis shared by the abutment element and the braking arm.