ABSTRACT. We study the dyadic model of the Navier-Stokes equations introduced by Katz and Pavlović. They showed a finite time blow-up in the case where the dissipation degree α is less than 1/4. In this paper we prove the existence of weak solutions for all α, energy inequality for every weak solution with nonnegative initial data starting from any time, local regularity for α > 1/3, and global regularity for α ≥ 1/2. In addition, we prove a finite time blow-up in the case where α < 1/3. It is remarkable that the model with α = 1/3 enjoys the same estimates on the nonlinear term as the 4D Navier-Stokes equations. Finally, we discuss a weak global attractor, which coincides with a maximal bounded invariant set for all α and becomes a strong global attractor for α ≥ 1/2.