A circulating fluidized bed boiler bottom slag waste heat recovery device comprises an L-shaped ash control valve (1), a sorting section pipeline (2), a cross-flow moving bed heat exchanger (3) and aslag discharging device (4), wherein the sorting section pipeline (2) is a big-end-up opening contraction pipeline, the upper portion of the sorting section pipeline (2) is provided with a sorting section inlet (2-1), and the lower portion of the sorting section pipeline (2) is provided with a sorting section outlet (2-2); the cross-flow moving bed heat exchanger (3) is composed of a separation flow guide plate (3-1), a cooling flue (3-2) and a bottom slag channel (3-3), the upper portion of a cross-flow moving bed is connected with the sorting section pipeline outlet through a slag feeding pipe (5), and the width of the bottom slag channel (3-3) of the cross-flow moving bed is 200-2000 mm; the bottom slag flowing speed is controlled by the slag discharging device (4), meanwhile, after being pressurized by a recycling fan, flue gas transversely passes through the bottom slag channel in an S shape through the separation flow guide plate (3-1), and the included angle (alpha) between theinclined section of the separation flow guide plate (3-1) and the horizontal direction is 20-80 degrees. According to the circulating fluidized bed boiler bottom slag waste heat recovery device, the recirculating flue gas is adopted as a heat exchange medium, the vast majority of heat of the bottom slag is recovered back into a boiler, continuous stable operation of the waste heat recovery deviceis ensured, boiler ash slag physical heat losses are decreased, and the boiler efficiency is improved.