The influence of coupling conditions of parallel-cascaded waveguide ring resonators on the time delay applications in the optically phased array antenna systems is analyzed. Two kinds of coupling conditions, over-coupling and restriction-free, are considered to achieve a certain target delay time by parallel-cascaded three ring resonators. The results show that the restriction-free coupling condition is better than the over-coupling one to obtain a flat time delay and amplitude response in the target delay bandwidth especially for the small target delay time, which is the advantage of ring-resonator-based tunable true time delay line.