Abstract: Floating mulch is a newly developed protected culture technology. The characteristics of air temperature, soil temperatures under covers were analysed by harmonic analysis and the growthes of vegtable with and without floating mulch were also compared.The day and night average air temperatures under floating mulch are higher about 7 ℃ and 3 ℃ than those without cover respectively in the spring at Beijing area. The average soil temperature from 0 cm to 30 cm of depth under floating mulch is higher 2℃ than that of control area. As the results of harmonic analysis, the time of occuring maxmum soil temperature under floating mulch is 30 min late.compared with that of control area at 10 cm depth.