A novel three-dimensional chaotic system with invariable Lyapunov exponent is proposed. The new system contains six system parameters, one quadratic cross-product term, and one square term. The dynamic properties of the new system are investigated via theoretical analysis, numerical simulation, Lyapunov dimension, Poincare diagrams, Lyapunov exponent spectrum, and bifurcation diagrams. The different dynamic behaviors of the new system are analyzed when each system parameter is changed. When the parameter of the square term varies, the Lyapunov exponent spectrum keeps invariable, the amplitudes of the signals of the first two dimensions change each as a power function with a minus half index, but the third one keeps its amplitude in the same range. Finally, the circuit of this new chaotic system is designed and realized by Multisim software, which confirms that the chaotic system can be achieved.