P wave time detection is one of the most important parameters in seismic calculations. Many attempts have been made to detect the arrival time automatically. However, manually detecting the P-wave arrival time is always important because this arrival time is used for automatic computational evaluation. Therefore. This study has been tried to improve the P-wave onset time detection, both manually and automatically, by providing a series of preprocessing on the seismic time series. In order to evaluate the proposed method, two stations of Sarab, and Azarshahr, which have more noise than Sarab station, were studied. The results showed that this method has a good performance in manually improving the P wave arrival detection.