Abstract: During the Luquan earthquake, two types of home-made strong motion selsmographs were used to monitor the strong aftershocks. 114 records of the strong aftershocks were obtained in total, in two of which the peak acceleration exceeds 0.1g. These two types of instruments are Model GQⅢ and Model Ⅲ-A three component strong motion seismographs with optical recording. In this paper, based on the actual observations, the working effect of these two types of instruments were analysed in two aspects: (1) the trigger start rate of the instruments for M_L ≥ 4 earthquakes; (2) the record quality. Finally, a preliminary discussions made for some principal problems on the records.