For the characteristics of wavelength and output power，discharge initiated repetitively pulsed HF laser has become the hotspot in mid-infrared laser device technology research field. In this paper, numerical simulation of flow field in discharge region and structure design of inject pipeline with repetitively pulsed HF laser device was described. Under the investigation of discharge characteristics in SF6/C2H6 gas mixture and output characteristics of laser pulse, the flow field uniformity and repetitively pulsed laser energy stability were researched. It is shown that with the optimized design of inject pipeline, the flow field uniformity improved obviously. The minimum flow velocity for gas circulation is elevated to 6.5 m/s. The deposited energy per unit volume gas with stable volum discharge increased from 1.6 J/ml?atm to 2.0 J/ml?atm. The maximal running frequency of 100 Hz and the average power of 40 W are obtained. The system operating stability keeps well.