The subwavelength metal slit changes in its transmittance properties if embedded with a groove inside.Red-shift,blue-shift or no shift may happen.In this work,we study the dependence of the transmission spectrum of slit on the depth of the embedded groove by using the finite difference time domain method.Compared with the results from cavity resonance mode theory,we find that the shift situation of the subwavelength metal slit comes from two reasons,the increase in the cavity length and the increase in the resonance mode number.The spectrum changes,such as blue-shift,are the hybrid results of the increase in both of the mode number and the cavity length.