The ash deposition problem of heat exchanger is a serious threat to the safety and stability of industrial production process, so it is necessary to strengthen the discussion on the ash deposition of heat exchanger. In order to investigate the deposition characteristics of fly ash particles in flue gas on the outer surface of the tube bundle heat exchanger, the particle deposition behavior in the process of flue gas flowing across tube bundle with a six-row tube arrangement is simulated. In this work, a numerical model is developed by considering the deposition and removal processes based on the software FLUENT, extended by user-defined functions. The Eulerian approach combined with dynamic mesh technique is adopted to explore the ash deposition characteristics. The deposition process takes into account four deposition mechanisms including the Brownian and eddy diffusion, gravity, thermophoretic, and turbophoretic. The deposition morphology after the net deposition mass reaches an asymptotic value is presented. By sorting out the particle volume fraction contours of different flow time, it is found that the vortices at the rear of the tube bundle swing back and forth in different flow directions, and the flow period is 8s. By comparing the deposition morphology and flow field distribution, it is found that the particle deposits are mainly concentrated in the low-velocity region. Then, the deposition characteristics of the particles on the surface of the tube bundle under different inlet velocity, particle concentration, and inlet temperature are examined. The influence of particle concentration and inlet velocity on deposition characteristics is obvious, while inlet temperature has little effect on deposition characteristics. This paper provides theoretical support for the formation and prevention of boiler ash deposition.