Measurement of fast signal is getting more and more important in many fields. In this paper, we propose to detect a temporal signal based on the idea of computational ghost imaging (GI), which can greatly reduce requirements on bandwidth of detectors. In experiments, we implement retrieving of a temporal signal with time scale of 50ns using a detector of 1kHz bandwidth, which is much lower than the requirement on bandwidth of detector according to information theory. The performance of our technique are also investigated under different detection bandwidths.