Flame instabilities of inclination and breakup for lean CH4/air combustion in porous media are studied experimentally and numerically. Inclination and breakup are observed in the quartz tube filled with alumina pellets of 3 mm in diameter for equivalence ratio range of 0.435-0.490. The effect of the equivalence ratio on the flame inclination and breakup are discussed and the results show that the equivalence ratio plays an important role on the breakup and flame inclination. Breakups always happen when the inclinational angle reaches 54-60 degrees. In order to explain the motivities of the inclination, a two-dimensional one-step chemical reaction, two-temperature model without initial angles are carried out to simulate the experimental cases. In order to check the possible motivities of inclination, we assumed profiles (not uniform) of inlet velocity of premixed gas and equivalence ratio at inlet, different porosities in the tube, half the same on the right, half on the left, in the simulations. The results show that the inhomogeneous inlet velocity gives slight influence on the inclination, but the different distribution of porosity and the inhomogeneous equivalence ratio at inlet give great influences on the inclination. Calculation results show that the heat loss have a significant influence in determining the flame shape at the initial moment and lead to an increase in the development of the inclination instability. At a low mixture velocity, hydrodynamic effect on the inclination instability is ignored, while the inclination angle of the flame front continually increases as the mixture velocity increase. (c) 2013 Elsevier Ltd. All rights reserved.