We study a three-dimensional quadratic autonomous chaotic system.Basic dynamic characteristics are analyzed via theoretical analysis and numerical simulation.Lyapunov exponent spectrum,Lyapunov dimension as well as bifurcation diagram are calculated.An electronic circuit is designed to realize the chaotic system.Relationships between system parameters and circuit parameters are built.The circuit is simulated using Pspice.Simulation results confirm the analysis.The system discussed is different from Lorenz system,Rössler system,Chen system and Lü system.The chaotic circuit is simple and practical.