An optical fiber sensing method was developed for prestress measurements of glass-metal seals. A fiber Bragg grating sensor was embedded in a hole in the sealing glass. The glass was then heated to melting, cooled and solidified so that the optical fiber sensor, the glass and the metal shell were sealed together. The fiber sensor gave real-time measurements of the sealing temperature during the sealing. The changes of the Bragg wavelength were used to measure the axial strain along the measurement path in the glass seal. The global stress distribution in the glass was then calculated by a finite element analysis. Tests show that the fiber sensor can monitor the temperature and stress during the sealing process and an optimized sealing process can be achieved by using prestress measurements in the glass as an indicator.