Laodongshan tunnel is located in typical “Dianzhong red strata”. During the construction of the tunnel, deformation and crack occur to the primary support. The deformation characteristics of the primary support are obtained by means of analysis on the monitoring data. The causes for the serious deformation of the tunnel in “Dianzhong red strata” are discussed in terms of rock mass lithology, groundwater, tectonic structures and construction management. Countermeasures, including strengthening the advance geology prediction, performing radial grouting, strengthening the primary supporting and controlling the duration and spacing of the construction process, are proposed. In the end, the deformation and cracking of the tunnel are brought under effective control.