Laser cladding technique has been applied on power station boiler tube against high-temperature corrosion and wear. However, in recent years, tube burst and cracking occurred frequently during long-term service after laser cladding. To explore the long-term service safety of laser cladding NiCrBSi coating, TP347HFG tube with NiCrBSi coating was prepared with a laser cladding system. These tubes were heat treated at 650, 750, 850, and 950 ℃ for 2000 h, separately. The influence of interdiffusion of elements between laser cladding NiCrBSi coating and TP347HFG tube on substate microstructure and microhardness was studied, which could provide a theoretical basis for subsequent safety evaluation. The evolution of microstructure and composition on the surface of TP347HFG were characterized by scanning electron microscope and energy dispersive X-ray spectroscope. The microhardness changes of TP347HFG substrates were tested by a microhardness tester. The results show that during the long-term service, the elements B and C in the coating diffuse into the TP347HFG substrate. In the substrate near the interface, carbides and boride phases with high Cr contents are precipitated in the interior and boundary of grains. With the increase in service temperature, the deeper the diffusion depth, the greater the size of the precipitation phases. The surface microhardness of the TP347HFG substrate increases with the increase in service temperature. The microhardness of the boiler tube at 50 μm near the interface changes with the increase in service temperature. The maximum hardness is 254, 299 and 417 HV0.2 after high-temperature service at 650, 750 and 850 ℃, respectively. The microhardness of this position drops to 376 HV0.2 after high-temperature service at 950 ℃ .