Aligning text-to-image (T2I) diffusion models with human preferences has emerged as a critical research challenge. While Direct Preference Optimization (DPO) has established a foundation for preference learning in large language models (LLMs), its extension to diffusion models remains limited in alignment performance. In this work, we propose an enhanced version of Diffusion-DPO by introducing a stable reference model update strategy. This strategy facilitates the exploration of better alignment solutions while maintaining training stability. Moreover, we design a timestep-aware optimization strategy that further boosts performance by addressing preference learning imbalance across timesteps. Through the synergistic combination of our exploration and timestep-aware optimization, our method significantly improves the alignment performance of Diffusion-DPO on human preference evaluation benchmarks, achieving state-of-the-art results.