A heating assembly for a respiratory treatment machine includes a base and a water tank. The base has a receiving space communicating with a recessed platform at a via an opening, and a heating plate securely placed on a bottom face of the receiving space. The water tank has a main receptacle, a secondary receptacle integrally formed and communicating with the main receptacle and movably received inside the receiving space, a conducting plate securely provided at a bottom face of the main receptacle and an extension integrally formed with the conducting plate and provided at a bottom face of the secondary receptacle. The extension has a dimension corresponding to that of the heating plate such that after the secondary receptacle is received inside the receiving space, the extension is placed on top of the heating plate and engaged with the heating plate.