The B-Δ method is examined to estimate an earthquake’s magnitude and epicentral distance from a single station in a short amount of P-wave data (3 s) for application in earthquake early warning systems. Fitting a simple function with the form of to the initial part of the waveform envelope, coefficients A and B are determined through the least-squares method. LogB is inversely proportional to logA, where Δ is the epicentral distance. B values are calculated on the basis of 26 vertical-component accelerograms of Qeshm earthquake with magnitude range Mw=5.3-5.5 and epicentral distances less than 43 and 16 km (Soza and Tonban station). By using this relation, we could estimate the epicentral distance by logA=-0.73logB+2.6. Earthquake magnitude estimated by empirical magnitude–amplitude relation that includes the epicentral distance as a parameter, is Mest=1.81log Pmax - 1.66logB +5.42. The greatest advantage of this method is its easiness and quickness.