For a case of constant-rate liquid production from a single well centered in a horizontal, homogeneous-acting, isopachous, and infinite reservoir, based on fundamentals of fluid flow in porous media the bottom hole flowing pressure never stabilize. In the process of field well testing, however, pressure values measured by the pressure gauge which has a definite resolution value will not change after a period, so the bottom hole flowing pressure can be considered to be stabilized. According to this situation, through theoretical derivation, a stabilized time formula is firstly proposed, by which the time after which the bottom hole flowing pressure measured with a pressure gauge will be stabilized can be calculated, and the stabilized time for a given pressure gauge is in direct proportion to the liquid producing rate, but in inverse proportion to the resolution ratio of the pressure gauge. Applied the stabilized time formula, a new formula of detectable radius can be derived, by which the effect of resolution of the pressure gauge can be considered. Secondly, the time after which the value of the pressure gauge measured in the bottom hole of the observation well starts to change during interference testing is obtained, and the time is related to the fluid flow rate and the distance between the producing well and the observation well. The conclusion can be applied as a reference in the design process of working system during well testing.