For the poor thermal-wet comfort property of present cotton/lycra elastic knitted fabrics, a kind of three-layer elastic knitted fabric with cotton yarn outside, superfine or special-shaped section filament inside and lycra in the middle was developed. This special structure made the fabric with good thermal-wet comfort property. The cotton yarn outside could absorb the sweat transmitted by the filament inside and release the sweat to the atmosphere to keep the skin dry. Under simulated human body sweating conditions, the dynamic changing curves of humidity and temperature in microclimate of the novel developed knitted fabrics were measured by a new instrument, sweating cylinder. Compared with the common cotton/lycra two-layer elastic knitted fabrics, the three-layer elastic knitted fabric have better dynamic heat & moisture transmitting property.