In this paper, a novel photonic digital-to-analog converter (PDAC) based on phase-change materials (PCMs) and electro-optic tuning microring resonators (MRs) is proposed, and the arbitrary waveform generation is realized. The PDAC uses MR array to process the optical signals of different wavelengths at the same time and integrates programmable phase-change materials into the optical waveguide to complete the power control of the optical signal and the power compensation of the electro-optic tuning MR, thereby realizing high-precision conversion of digital signals into analog signals. A 4-bit PDAC structure is simulated with 25 GSa/s input data rate using the Ansys Lumerical simulation platform. The proposed PDAC can achieve an effective number of bits of 3.63 bit, and the maximum integral nonlinearity (INL) and maximum differential nonlinearity (DNL) are 0.88B_LSB (B_LSB represents least significant bit) and 0.35B_LSB, respectively. In addition, the proposed PDAC can realize the generation of square wave, sawtooth wave, triangular wave, and sine wave with small error compared to idea waveforms. Simulation proves that the proposed structure will be used in digital-to-analog converters and arbitrary waveform generators with high speed and low conversion error.