To meet the demands for various applications in optical filtering and microwave signal processing, integrated silicon photonic filters are required to be multifunctional, reconfigurable and tunable. In this work, an integrated multi-functional optical filter is proposed, which is designed based on a tunable Sagnac loop reflector and a microring resonator. The through port and drop port of an add-drop microring resonator are connected with the two ports of a tunable reflector. By controlling the thermal phase shifters in different scenarios, the device can be reconfigured into a reflective-type asymmetric Mach-Zehnder interferometer filter, a reflective-type all-pass microring resonator filter and self-interference microring resonator filters. An analytical model is established based on the transfer matrix. The simulation results show that the device can achieve the following functions: sinusoidal spectral filtering with four different free spectral ranges, Lorentzian spectral filtering toggling between band pass and band stop, and spectral reconfigurations of Fano resonance, electromagnetically induced transparency, and electromagnetically induced absorption. Each spectrum mentioned above can be tuned fast and widely. Reflection provides a new degree of freedom in design, breaks through the inherent footprint limit, and achieves a wide range of free spectral ranges. Our proposed tunable Sagnac loop reflector assisted microring resonator provides a new scheme for realizing flexible, tunable and multi-functional reconfigurable integrated photonic filters, and has broad applications in the integrated photonic analog signal processing and microwave photonics.