In order to improve descaling efficiency and heat transfer performance of shell and tube heat exchanger, a gas-fired lithium bromide absorption chiller is selected as the research object. By installing rubber ball online cleaning system, the influence of rubber ball online cleaning on the heat transfer performance of absorber and heat exchanger was experimentally studied. The results show that the fouling resistance of heat exchanger increases with the increase of operation time while the performance coefficient (COP) of direct-fired unit decreases with time under the condition of no rubber ball online cleaning system. The ball rate, service time and start /stop ratio of on-line cleaning system have significant effects on fouling resistance of shell and tube heat exchanger. When the input rate is 10%, 20%, and 30%, the thermal resistance of the scale increases by 32.8%, 20.8% and 8.9%, respectively. When the running time is 20 s, 40 s and 60 s respectively, the thermal resistance of the scale increases correspondingly by -20.8%, 17.9% and 10.7%. When the start-stop ratios are 1:1, 1:2 and 1:3 respectively, the thermal resistance of scale increases correspondingly by 16.1%, 23.0%and 29.0%. With the running cost and the service life of the rubber ball taken into account, the best working condition is when the input rate is 20%, the running time is 60 s with an interval of 120 s, and the start-stop ratio is 1:2.