Aiming at the statistical distribution of azimuth detection of ultra-short-range incoming targets, this article studies the influence mechanism of periodic scanning magnetic signal on the detection accuracy of the laser-magnetic composite azimuth measurement method. The mathematical model of the permanent magnet rotating scanning space magnetic field is formulated, and the periodic scanning magnetic signal equation is derived. Combined with the characteristics of the magnetic signal and the constant threshold time measurement method, the analytical formula of the probability and statistical distribution function of the time measurement of the periodic scanning magnetic signal is deduced. The effects of scanning period, magnetic field intensity, threshold voltage, and noise on the probability and statistical distribution of time measurement are studied. The results show that with the increase in scanning period and magnetic field intensity, the symmetry of the probability distribution function is not affected, the half-width of probability distribution decreases, and the peak value of distribution increases in the range of 0. 75~ 1. 88. With the increase of the threshold detection voltage, the probability distribution firstly shows a trend of decreasing half-width and the peak value is increased by 0. 48, then increasing halfwidth and the peak value decreased by 0. 54, and the rising and falling edges of the distribution curve before and after the peak have different trends. With the increase of equivalent noise voltage, the symmetry of the probability distribution function is not affected, but the distribution half-width increases and the distribution peak decreases in the range of 0. 4~ 0. 48.