This thesis used 7 celery lines from Agronomy and Biotechnology college of CAU. growth under natural heat stress and heat damage index is studied on the celery lines which are classified into three levels(heat-tolerant, intermediate and heat-sensitive). And then the celery seedings were put under two high temperature treatments, 26℃/20℃（d/n）and 30℃/20℃（d/n）, respectively. After the treatments, the contents of free protein and resolvable sugar were assayed by means of spetrophotography. The relationship between the physiological and biochemical characters and the heat resistance of celery was discussed. The results are as following: Heat damage index and relative growth under the temperature of 26/16℃ showed significant correlation with heat tolerance. Both of them can be used to determine the heat-tolerant ability of celery lines, which can be most quick and convenient. The free protein and resolvable sugar showed unconspicuous correlation with heat tolerance.
