Abstract: It is very important for eco-environmental construction in western Liaoning to study the drought resistance mechanism of trees, breed drought resistant varieties, and improve drought resistant afforestation technology. Being the research objects in this study, Armenniaca sibirica, Robinia pseudoacacia, Quercus mongolica, Acer truncatum and Cotinus coggygria are broadleaf tree species and have important ecological value in western Liaoning. In the growing season, we determined and studied the photosynthetic physiological characteristics which would be the physiological base of these trees’ drought resistance. The main results were as follows: the average photosynthetic rate value order of the five tree species from high to low was Armenniaca sibirica, Acer truncatum, Cotinus coggygria, Quercus mongolica and Robinia pseudoacacia, showing that Armenniaca sibirica had higher potential photosynthetic productivity than other species. The order of average stomatal conductance value from low to high was Robinia pseudoacacia, Armenniaca sibirica, Quercus mongolica, Cotinus coggygria and Acer truncatum, showing that Robinia pseudoacacia and Armenniaca sibirica had stronger ability to prevent water loss from stomatal, and they had an excellent foundation of drought resistance. The order of average transpiration rate value from low to high was Robinia pseudoacacia, Armenniaca sibirica, Quercus mongolica, Cotinus coggygria and Acer truncatum, showing that the water losing amount of Robinia pseudoacacia and Armenniaca sibirica was less in the unit time, and the two species had higher WUE.