Abstract: In this paper we described a study on delayed ion extraction in laser desorption/ionization time of flight mass spectrometry which gives us a much higher mass resolution compared with the previous continuous mode.By computer modeling and carefully selecting the parameters such as delayed time and voltage ratio(extracting volt/repelling volt),we have obtained mass resolution up to 1734(reflect mode)with gramiciding(α cyano 4 hydroxycinnamic acid as matrix) and 2124 with insulin(4HCCA as matrix)on our modified laboratory built instrument.