This paper highlights the importance of building a reliable AI-generated text detection system, given growing concerns about the potential misuse of large-scale language models. We highlight the limitations of existing methods, which overlook style modeling and rely on static thresholds, significantly limiting detection performance. We propose the Mixture of Stylistic Experts (MoSEs) framework, which enables conditional threshold estimation for quantifying style-aware uncertainty. MoSEs consists of three core components: a Style Reference Repository (SRR), a Style-Aware Router (SAR), and a Conditional Threshold Estimator (CTE). For input text, the SRR activates appropriate reference data and provides it to the CTE, which then dynamically determines the optimal threshold by jointly modeling linguistic statistical and semantic features. MoSEs generates predicted labels with discriminant scores and corresponding confidence levels, achieving an average 11.34% improvement in detection performance compared to existing methods, and a 39.15% improvement in low-resource environments. The source code is available on GitHub.