The cloud lidar, with the character of high precision and good stability, is an effective way to detect the cloud height. Pulse diode laser(PLD), as an essential part of the lidar system, needs the triggering pulse. In this paper, the emitting part of the lidar was studied, including the simulation of the backscatter SNR, choosing of PLD and design of trigging circuit to drive the 905 nm PLD with the consideration of the optical system. A circuit for trigging the laser pulse with adjustable power and pulse width was contrived. Then the software Systemview was used to emulate the design and finally the making of PCB was finished. The results show whatever the parameters of the pulse, namely trigging pulse width, the rising edge, dithering, all these can be qualified to be in use in practice and enjoys the merits of low cost and convenience. The emitting module operates well.