The invention relates to a transitional glass rod and a preparation method thereof. The transitional glass rod is characterized in that basic glass of the transitional glass rod is a SiO2-B2O3-Na2O glass system, wherein the basic glass comprises the following components: 60-75wt% of SiO2, 15-30wt% of B2O3 and 6-15wt% of Na2O. The preparation method of the transitional glass rod comprises the following steps: mixing according to the components of the basis glass, melting, forming a glass rod by drawing after glass is clarified and homogenized, and then carrying out heat treatment, acid treatment and ultrasonic cleaning, so as to obtain a cleaned glass rod; and immersing the cleaned glass rod into borax solution for carrying out permeation and adsorption of sodium ions, then drying, and sintering, so that the transitional glass rod is obtained. The transitional glass rod provided by the invention has the advantages that thermal expansion coefficient of transitional glass is between that of quartz glass and that of a metal electrode, stress during sealing of the quartz glass and the metal electrode can be effectively relieved, and product quality is improved.