This paper presents the vibration characteristics of a rectangular plate with 45$^{circ}$oblique crack and a smooth plate subjected to a uniaxial tension. The experiment is adopted by the time-average holography method. The natural frequency and mode shape are considered accurate according to the increasement of tensile load in the study. When tensile load is zero, the vibration modes are almost agreed with the smooth and the 45$^{circ}$obliquely cracked plate. But since then, according to the increasement of load, it is shown that vibration modes are extremely varied. The effects of the crack length in the vibration characteristic are discussed in detail. It is indicated that the increase of the crack length makes the variation of the frequencies and modes complicate in the range of even a small load.