The elastic properties of Tetra-polyethylene glycol (PEG) gel, a four-armed PEG network gel, were studied by simulating the deformation of elastic networks containing defects that are randomly introduced to the network. This network model accurately reproduced the experimental results observed for Tetra-PEG gel. In particular, the stress-extension ratio curve of the gel prepared at chain-overlap concentration was in agreement with that of a regular network without defects. As the defect density increased, the Young’s modulus decreased linearly. The fracture and spatial inhomogeneity of the networks were also investigated in the simulation. The elastic properties of Tetra-polyethylene glycol (PEG) gel, four-armed PEG network gel, are studied by simulation for deformation of elastic networks containing defects randomly introduced to the network. This network model well reproduces the experimental results of Tetra-PEG gel. In particular, the stress-strain curve of the gel prepared at chain overlap concentration agrees with that of a regular network without defects. As the defect density increases, the Young’s modulus linearly decreases. The fracture and spatial inhomogeneity of the networks are also investigated by the simulation.