Abstract: Slash pine is one of the important tree species which were used to build up the protective forest in the coastal area in southeast of China.Its photosynthetic characteristics and net photosynthetic rate in different mixed forests were measured with Li6200 photosynthetic system in Dongshan Chishan Protection Forest Farm of Fujian province.The results were as follows:its CO2 compensation point was 163 μmol/mol,carboxylation efficiency was 0.017 1,dark respiration was 0.28 μmol/(m2·s),light compensation point was 40 μmol/(m2·s),and light saturation point was 1 100 μmol /(m2·s);The daily course of net photosynthetic rate of leaves in superstratum and in substrate had two peaks,and the leaves in superstratum were more important than that in substrate for photosynthesis;In order to increase its photosynthetic efficiency,slash pine should be planted more than 3～4 rows for each strip when making stripmixedforest with Casuarina;The net photosynthetic rate of slash pine planted under the sparse shelterbelts was studied also,and the results showed that it should be regarded as one of the regeneration methods to plant slash pine under the sparse shelterbelts whose shade density is less than 0.28.