An i ntegrated silicon nitride waveguide microring resonator based on thermo-optical effect is designed and fabricated.The device adopts the tunable coupler constituted by th e Mach-Zehnder interferometer(MZI) which controls the coupling ratio to tune the extinction ratio.Besides,the size of waveguide,bend radius,the gap size in the coupling region and other parameters a re designed and optimized.Two silicon nirtride waveguide microring resonators with different ben d radii are fabricated by the lithography,reactive ion etching(RIE)and other micro fabrication processe s.The experimental results show that around the wavelength of 1550nm,the free s pectral range,3dB bandwidth,Q factor, tunable range of the extinction ratio are 68pm,16pm,9.68×10⁴,and 17dB,resp ectively.The research of this tunable microring resonator filter is very promising for the optical communicati on and the microwave photonic filtering.