On the basis of theoretical calculation of one-dimensional pulse-response model of the Rayleigh backscattering in a singel mode fiber, theoretical simulations of Rayleigh waveforms for 1550 nm of nanosecond pulses in 80 m fiber in a phase optical time domain reflectometer (OTDR) are presented. By changing physical parameters such as refractive index, laser frequency and pulse width, relations between waveforms and the physical parameters are given. With the increase of optical fiber′s refractive index, the drifting quantity of the first Rayleigh peak increases and the Rayleigh peak density decreases; with the increase of the laser frequency, the drifting quantity of the first Rayleigh peak shows a periodic attenuation oscillation, and the Rayleigh peak density increases accordingly; with the increase of the pulse width, the drifting quantity of the first Rayleigh peak dispalys a periodic attenuation oscillation, the Rayleigh peak density decreases, and the peak power increases.