Abstract: Studied here in the paper is the regularity of the influence by the specimen thickness and span on CTOD test result of the X80 pipeline steel. The result shows that during the CTOD test to the X80 pipeline steel，the CTOD value increases along with increase of the specimen thickness，and on the contrary decreases along with increase of the specimen span. And during the said CTOD test，the specimen thickness needs to be as close as possible to the actual steel pipe wall thickness so as to ensure that the test result can much more reflect the actual status of the steel pipe. The span value must be strictly determined according to the applicable standard，and mustn’t be arbitrarily changed.