The consistence of performance such as excess loss, coupling ratio and drawing length of fused fiber couplers is poor, even if they are fabricated at the same technical parameters; And the fused temperature provided by gas fluctuates by 5-30°C, while the drawing speed is rather stable. To find out the reason of poor performance consistence, the rheological numerical analysis is carried out under the non-isothermal condition. The effect of technology parameters such as drawing speed and fused temperature on the fabrication process is studied. A conclusion can be reached that it is the fluctuation of fused temperature that induces poor consistence. An electrical resistance microheater is designed and fabricated, and its fluctuation of temperature is by 1.5°C. The performance consistence of fibre coupler is improved greatly with the novel heater.