A slide-track buffering device with a smoothly sliding carriage comprising: a control stand on which there are a guide plate extending forward, a guide chute at the rear part of the guide plate, and a beveled resisting groove in front of the guide chute; a slide carriage sliding on and covering the guide plate and comprising a shorter first area in the back, a locator under the first area, and an accommodating groove in front of the locator; at least a spring unit linking between the control stand and the slide carriage; a swing member which is held in the accommodating groove and located between the slide carriage and the control stand and is provided with a joint hole in the back and a boss underneath in order to engage the locator with the joint hole, accommodate the boss in the guide chute and embody superior smoothness and actuation.