The present invention relates to a method for accurately calibrating fusion temperature in optical fiber splicing. With assistance of direct arc-recentering technique, two optical fibers are spliced and then continuously heated with a post-fusion process. In the process, the fusion temperature is automatically determined in terms of effective fusion currents, which is done by real-time monitoring the fusion time dependence of cladding diameter reduction. In comparison with model calculations, variations of fusion temperature caused by changes of electrode condition and operating environment, e.g. altitude, temperature and humidity are derived. To recover the optimal fusion temperature in various fusion processes, the calibrating results are automatically invoked to compensate fusion currents.