Mass resolution of a time‐of‐flight mass spectrometer with a two‐stage electrostatic reflector is calculated for secondary neutral mass spectrometry. The instrument parameters are optimized for energy and space focusing: correcting the flight time difference due to the energy width &Dgr;Eof sputtered particles and the spatial width &Dgr;sof an ionizing laser beam. The effect of &Dgr;scan be compensated by applying an acceleration field to the ionizing region, and the maximum resolution becomes about 1000 for &Dgr;E=10 eV and &Dgr;s=1.0 mm.