We propose a valley filter based on 8-Pmmn borophene which hosts two tilted Dirac cones. It is found that the application of a magnetic-electric barrier provided by a single ferromagnetic gate is sufficient to create valley-polarized current in 8-Pmmn borophene. The valley polarization of output current depends on the barrier orientation. Due to an intrinsic symmetry, it vanishes when the barrier orientation is along the tilted direction of Dirac cones. For the barrier orientation perpendicular to the tilted direction, the valley polarization for a realistic magnetic barrier can approach nearly 100% at proper Fermi energy and gate voltage. The remarkable valley contrast of conductance in this case is attributed to a new transmission resonance. The tilting of Dirac cones is essential for the predicted valley filtering. Our findings are helpful for valleytronic applications of two-dimensional materials with tilted Dirac cones.