Based on the basic principles of tapered optic fiber transmission, this paper primarily analyzes the transmission characteristics of fused tapered optic fiber which is coated with refractive index-matching fluid versus the index-matching liquids′ temperature variations. The transmission loss curves of computer simulation and experiment are very close in tendency. The results show the relationship between the transmission characteristics of tapered optic fiber and the temperature changes. With the temperature increment of outside ambient, the refractive index of index-matching liquids declines. Based on this, the ratio of the optical power carried by the tapered fiber to the total optical power increases. As a result, transmission loss is reduced. Based on the transmission characteristics of this optical device, a temperature-controlled short-pass filter is proposed, the cut-off wavelength of this filter becomes longer with the temperature increased. The rejection efficiency can be above 35 dB and the temperature coefficient of this filter is 40 nm/℃.