The invention discloses a two-dimensional magnetic optical trap 
system and a narrow 
line width single photon source preparing method thereof. The 
system comprises two pairs of reversed Helmholtz coils, a 
quartz vacuum cavity, an 
ion pump, a current feed through part with 
alkali metal releasing agent, a vacuum valve, a six-way connector, a first 
glass window, a second 
glass window and a first 
semiconductor laser. Six openings of the six-way connector are respectively connected with the 
quartz vacuum cavity, the 
ion pump, the current feed through part, the vacuum valve, the first 
glass window and the second glass window. The two pairs of reversed Helmholtz coils are respectively arranged in a horizontal-symmetrical mode and in a vertical-symmetrical mode. According to the method, the two-dimensional magnetic optical trap 
system obtains a long-strip-shaped cold 
atomic group through cooling light, then spontaneous 
radiation four-wave mixing is used, Stokes photons and reversed Stokes photons are generated through pump light and 
coupling light, and the photons are collected. The 
line width of a narrow 
line width single photon source prepared by the two-dimensional magnetic optical trap system is in the megahertz magnitude, and the narrow line width 
single photon source is suitable for long-distance 
quantum communication.