As　one　of　the　most　promising　clean　alternative　fuels,　natural　gas　has　been　widely　used　in　automobile　engines.　However,　due　to　the　slow　burning　velocity　of　natural　gas　and　its　poor　lean-burn　ability,　hydrogen　is　often　added　to　improve　its　combustion　behavior.　Researches　on　the　fundamental　laminar　premixed　flame　characteristics　of　CH4/H2blends　are　of　great　significance　to　understand　the　combustion　process　in　practical　combustors.　The　intrinsic　instability　of　laminar　flame　is　one　of　the　classic　issues　in　flame　dynamics,　which　presents　the　dynamic　response　of　laminar　premixed　flamelets　to　weak　perturbations.　By　studying　dynamic　mechanism　of　intrinsic　instability,　we　can　estimate　the　burning　velocity　more　accurately　and　gain　a　deeper　insight　into　the　turbulent　combustion　process　in　spark　ignition　engines.　In　this　study,　the　cellular　instabilities　of　laminar　premixed　CH4/H2/air　flat　flames　were　studied　using　McKenna　burner　with　OH-PLIF　technique.　It　was　found　that　the　addition　of　H2　can　broaden　the　lean　combustion　limit　on　flat　flame　burner　with　which　the　cellular　instabilities　were　brought.　The　digital　and　OH-PLIF　images　were　obtained　to　calculate　the　quantitative　parameters　of　cellular　length　scale,　which　is　associated　with　the　properties　of　fuel　mixtures　such　as　Lewis　number,　Markstein　number　et　al.　Through　the　theoretic　analysis,　we　make　a　thorough　investigation　on　the　mechanism　about　how　the　cellular　scales　were　determined.