The precise control of the thermal splicing temperature of ZBLAN fiber and silica fiber was guaranteed by theoretical simulation, analysis, and experimental optimization. The thermal splicing model was established, and optimized thermal splicing parameters were obtained based on the simulation results. The thermal splicing parameters were finely repeatedly tuned and optimized further in the thermal splicing experiments according to simulation parameters. The achieved loss was measured to be about 0.3 dB in the thermal splice experiments. The offset thermal splicing method demonstrated a repeatable, low-loss, and promising technique for the splice of ZBLAN fiber to silica fiber.