Quartz-enhanced photoacoustic spectroscopy （QEPAS） was first proposed in 2002 and has emerged as a landmark technique for trace gas detection. This technique employs a quartz tuning fork （QTF） as the acoustic transducer， replacing the broadband microphone used in conventional photoacoustic spectroscopy （PAS） systems. QEPAS not only preserves the intrinsic advantages of conventional PAS， such as wavelength-independent operation and zero-background detection， but also offers significant improvements in system integration， cost effectiveness， immunity to electromagnetic interference， and detection sensitivity. Over the past two decades， QEPAS has undergone rapid development， with detection limits for various target gases reaching the part-per-billion （ppb） level. This review systematically summarizes the physical mechanisms and fundamental principles of QEPAS， and further discusses several key innovation directions， including the integration and optimization of advanced laser sources， the design of custom tuning forks， and the performance enhancement of acoustic micro-resonators. On this basis， the major technical bottlenecks and challenges currently faced by QEPAS are analyzed， and future development trends are discussed.