Abstract: Heat stress is an important factor which influences agriculture. Responses of ABA, Ca2+, salicylic acid(SA) and jasmonic acid(JA ) to heat stress and their relations are reviewed. Heat stress increases the content of ABA, Ca2+, SA in plants; moreover, external applied ABA, Ca2+, SA and JA enhance thermtolerance. Ca2+ enhances the activities of SOD, CAT, APX and level of calmodulin as a second message. ABA induced the thermtolerance of plant mediated by Ca2+ in cytoplasm. SA is considered to be a message molecule to stress. H2O2 is probably a part of the signal cascade of SA that induces thermtolerance. JA excutes its function by itself or by increasing ABA. JA and SA have common or contrast physiological functions, but their signal transduction pathways differ. Further research ideas for signal transduction of heat stress are suggested.