An innovative high-efficient 1.3 kW open sorption thermal storage (STS) prototype using multilevel cascade reactors is experimental investigated for space heating. It can solve the performance degradation problem of traditional STS systems, by cascading two reactors which was packed with activated alumina/LiCl composite and SrBr2·H2O, respectively. Its performance under different relative humidity (60%, 80% RH) and flow rate (30, 39 m3/h) of inlet air at 20 oC were tested, whose results were compared with that of the same size reactor packed with only activated alumina/LiCl composite. The results prove that the cascaded reactor with different sorbents can increase the storage density from 191 kWh/m3 to 252 kWh/m3 under the condition of 20 oC and 80% RH. It also indicates that the output temperature (from 35 to 40 oC) and power (from 120 to 200 W) can be adjusted by changing the relative humidity and flow rate of the inlet air.