[en] The Superconducting Super Collider Accelerating Complex consists of a cascade of accelerators and each one of them accelerates the beam to some energy and then transfers it to the next stage. The design luminosity of 10³³cm^-2s^-1 is obtained by the high efficiency of all stages and the ability to accelerate beam with as minimum emittance growth as possible. For this purpose the Linac pulse length is specified as 9 ps in order to minimize the number of target crossings and so to minimize the emittance growth during charge exchange injection into the LEB booster. However, the transient caused by switching on the beam makes up a significant part of the pulse length and can influence the characteristics of beam. In this paper we present the results of the transient study of the coupled cavity linac and discuss the model that predicts the parametric resonance between the beam and the field distortion setup during transient