According to the heat conduction theory，different sections of the cladding of microstructured fibres (MSF) have different temperature in the high temperature zone during drawing MSF. The temperature decreases gradually from the surface to the central in MSF preform，and the temperature gradient will increase with either the increase of feed speed of MSF preform or decrease of the air-filling fraction. Because both the surface tension and the coefficient of viscosity are functions of temperature，when the MSF preform is thinned to MSF，the actual structure of MSF is not a simple down-sealing of the perform. The shrink size of the air holes will increase as the temperature rises. In order to obtain the MSF as expected，we must design the size of air holes of the MSF preform to vary corectly with the temperature variations，so as to effectively eliminate the effects of uneven heating temperature on the air holes in the cladding of MSF.