The ultrasonic-assisted extraction process of flavonoids from Cardiocrinum cathayanum (E.H.Wilson) Stearn bulbs (CCBF) was optimized, and the in vitro antioxidant and acetylcholinesterase (AChE) inhibitory activities of CCBF were investigated. Using C. cathayanum bulbs as the raw material, single-factor experiments were conducted to evaluate the effects of six parameters—ultrasonic power, ultrasonic mode, extraction time, extraction temperature, number of extraction cycles, and ultrasonic frequency—on the extraction yield of CCBF. The Box–Behnken response surface methodology was employed to determine and validate the optimal ultrasonic extraction conditions. The in vitro bioactivities of CCBF were assessed through antioxidant assays and AChE inhibition experiments. The results showed that the optimized extraction conditions were as follows: ultrasonic power of 1 000 W, ultrasonic mode of 6∶1 (on-time (s)∶off-time (s)), ultrasonic frequency of 40 kHz using an 8 mm probe, and three extraction cycles. Under these conditions, the extraction yield of CCBF reached 105.52 ± 0.65 mg/g. Antioxidant assays demonstrated a clear dose–response relationship across multiple systems, with IC₅₀ values of 0.41, 0.60 and 0.97 mg/mL against DPPH, ABTS, and OH radicals, respectively. In the FRAP assay, the reducing capacity of 0.60 mg/mL CCBF was approximately equivalent to that of 0.10 mg/mL FeSO₄. The AChE inhibition assay, performed using a modified Ellman method, showed inhibition rates of 80.74% ± 1.49% and 61.31% ± 2.01% at CCBF concentrations of 1.00 and 0.25 mg/mL, respectively. This study provides a foundation for the high-value utilization of C. cathayanum resources and offers insights for subsequent isolation, identification, and lead compound discovery of its active constituents.