The photonizing research is the development trend of phased array radar. Due to its excellent characteristics on the integration level and optical properties, the photonic crystals have extensive application prospect in the photonics research of optical true time-delay lines phased array radar. Based on the slow light characteristics and thermo-optical modulation theory, optical true time-delay lines applied in beam forming network of phased array radar are proposed. By optimizing parameters of the photonic crystal slow waveguide, high accurate modulation of of photonic crystal designed ranging from 0 ps/mm to 36.69 ps/mm is achieved. Meanwhile, the delay bandwidth larger than 23 GHz is realized. By optimizing variation characteristics of the group velocity with temperature, the time delay variation is in the range from 0.36 ps/mm to 1.57 ps/mm whenever the temperature changes 1 ℃. The optical true time-delay lines based on photonic crystal proposed can achieve highly efficient and accurate modulation on the delay. Compared with the traditional electrical domain beam-forming network, it has the advantages of high integration, wide instantaneous bandwidth and high tuning accuracy, which can provide a theoretical basis for the beam-forming network research of the high frequency wideband phased array radar.