In the double-cone ignition scheme, two deuterium–tritium shells in a pair of head-on Au cones are compressed and accelerated spherically [Zhang et al., Philos. Trans. R. Soc. A. 378 (2184), 20200015 (2020)]. The high-speed plasma jets from the cone tips collide and form a stagnating plasma with a higher density and higher temperature during the stagnation stage. The preheated plasma is then rapidly heated up further to the ignition temperature by fast electrons generated by a powerful laser pulse of 10 ps. The conditions of the stagnating plasma strongly affect the fast-heating efficiency and consequently the success of ignition. In order to understand dynamical process in the stagnation stage, a special experimental campaign was conducted, where the evolution of the stagnating plasma was diagnosed through the temporal resolved self-emission signals. The spatial-temporal distributions of temperature and density of the colliding plasma were analyzed by the Abel inversion algorithm and the Legendre polynomial fitting. The stagnation period was found to be about 300 ps, the temperature of the core area of the stagnated plasma was between 340 and 390 eV, while the aspect ratio of the colliding plasma was about 0.78. The central area of the colliding plasma has high temperature and high density simultaneously, which would benefit the consequent heating process according to analytical calculations.