Influenced by the wake flow of upstream cylinder, the downstream cylinder is prone to wake-induced vibration at small wind angles. Although fluctuating lift is closely related to wake-induced vibration, the characteristics of fluctuating lift are less investigated, and the flow field mechanisms are not yet clear. For two staggered circular cylinders with center-to-center pitch ratio P/D of 1.5-4, by using the large eddy simulation (LES) method, the intrinsic relationships between the fluctuating lift of the cylinders and the flow fields were studied at small wind angles (β=0°-30°) with a high Reynolds number of Re=1.4×10⁵. The interference mechanisms between the two cylinders were explored based on the flow field mechanics. Results show that the fluctuating lift of the cylinders and the flow field mechanisms experienced significant changes at small wind angles, and there were five different interference flow patterns, namely, wake interference, shear layer interference, proximity interference, interaction between vortex and cylinder, and interaction between vortex and vortex. Under wake interference and shear layer interference, the fluctuating lift of the downstream cylinder was much smaller than that of a single cylinder. Under proximity interference, the interaction between the two cylinders was weak, and the fluctuating lift of the downstream cylinder was close to that of a single cylinder. For the interaction between vortex and cylinder and the interaction between vortex and vortex, the fluctuating lift of the downstream cylinder was higher than that of a single cylinder, and the wake vortex impinging of the upstream cylinder on the downstream cylinder or the interaction with the downstream cylinder led to the rapid increase of the fluctuating lift of the downstream cylinder.