Abstract：In 2 environment conditions of open field and greenhouse，in spring and summer 2 cultivation seasons，the agronomic traits of 110 accessions of lettuce（Lactuca sativa L.）germplasm were investigated．At the same time，the heat tolerance was evaluated by the center column length，number of bolting days and the index of heat injury．The results showed that the leaves traits of no-heading lettuce tip，leaf shape，leaf color，plant height，petiole length，stem thickness，plant weight and fresh-cut vegetables weight all varied greatly，showing that the no-heading lettuce bears great potential in germplasm variation and innovation ability．Heading lettuce varieties have a higher similarity．Only in the petiole thick，rosette leaves，fresh-cut vegetables weight（head weight），there is a big variation．In early summer，the no-heading lettuce bolts 12-36 days earlier than the spring，and the heading lettuce bolts 18-38 days earlier．In greenhouse under strong high temperature stress，the no-heading lettuce bolts further ahead of schedule，and 82% of them bolt within 10 days，showing sensitivity to high temperature．Some heading lettuce varieties die of heat injury．The heat injury index can accurately reflect the heat tolerance between varieties of heading lettuce．The number of bolting days，center column length and single plant weight，head weight，leaf /shape ratio，etc. show remarkable correlation. They are also important indicators to evaluate the heat tolerance of lettuce．In spring greenhouse cultivation，the heat tolerance of lettuce germplasm resources are preferably evaluated by heat injury index and the number of bolting days．
