The design and the construction of a intracavity intensity enhanced continuouswave CO2 laserwith line selected by concave grating are described,which is suitable for photochemistry in its op tical resonator. 53 rotational lines in the 000 ～100 0 band and 49 rotational lines in the 000 1～020 0 band have been obtained,which are ascribed to the long op tical resonator and higher gain. The op timum design parameters of the laserwith the aim of obtaining the maximum intracavity power are given. The output power of lowestgain line 10P (56) is 2. 5W, and the power in the op tical resonator is about 166. 7W. The strongest power in the op tical resonator occurs at P (20) for the 000 12100 0 band with 520. 3W.