Based on the scalar theory, the influence of the blazed transmission grating with different groove angles or different groove densities on the used wavelength was researched and the energy distribution of the diffraction light of the blazed transmission grating was deduced. It was concluded that the relationship between the diffraction angle and the incident angle of the diffracted grating in the diffraction direction with the strongest energy could satisfy the Snell's law. The relationship among the angle of incidence, diffraction angle and groove angle was given, and the energy distribution law of the diffracted light at different groove densities and groove angles was studied. Then, the blazed transmission gratings were measured. It is shown that the characteristics of the existing blazed transmission gratings are consistent with that of theoretical calculation. A polydimethylsiloxane (PDMS) period-tunable blazed transmission grating was fabricated. Then, the blazed wavelength and groove density of the PDMS blazed transmission grating were measured in both stretched and free state by using the deduced formula. The results show that the measurement error of the wavelength is within 5 nm. The equivalent groove profile of the grating was fitted, which verifies the law that groove profile and groove density of the PDMS grating are changed with the tension changes in the real-time monitoring.