A concept of degree of comprehensive network connectivity (DCNC) is proposed in order to study the communicational connectivity between different ground users in the service area of a communication constellation. As an important part of availability of service (AoS), DCNC should be a pivotal specification of communicational systems and play a leading role in the top design of systems. First, the relevant definitions of DCNC are proposed, based on which a DCNC evaluation model is established which takes into consideration the inter-satellite link constraints and coverage constraints in a LEO mobile communication constellation. Using the model, simulation and analysis for DCNC variation are performed in different constellations by altering the orbital heights and orbital inclinations respectively. The simulation results indicate that both orbital inclination and orbital height have notable effects on DCNC, and that reducing the number of orbital planes properly is advantageous to the improvement of DCNC. The conclusions can help select the optimal constellation configuration parameters in the concept design phase.