Recent studies have found that the optical maturity (OMAT) and the mean grain size of the lunar regolith have latitude dependences (Hemingway et al. 2015, Icarus; Jeong et al. 2015, ApJS), probably because of the reduced flux of space-weathering agents at high latitudes. Here we extend these works to the inner walls of lunar impact craters, dividing a wall into four quadrants, the North, South, East, and West. We consider 3,746 craters whose latitudes are between −50° and +50° and whose diameters are between 5 km and 120 km in the Lunar Impact Crater Database 2015 from the LPI. We adopt the topography-corrected OMAT data from the Kaguya/MI observations (Lemelin, personal communication). The OMAT differences between the N and S walls in a crater are insignificant near the equator, but at high latitudes, the equator-facing walls have generally smaller (more mature) OMAT values than the pole-facing walls. This trend confirms that the incoming direction of the space-weathering agents is predominantly along the ecliptic plane. The longitudinal curve of the mean [OMAT(E) − OMAT(W)] value is sinusoidal and has a minimum and maximum near longitudes −60° and +60°, respectively. We assert that this is due to the shielding of solar wind particles during the Moon’s passage through the Earth’s magnetotail. We present a simple toy model to show that the shielding by the Earth’s magnetotail is indeed responsible for the sinusoidal behavior of the [OMAT(E) − OMAT(W)] curve. This implies that the dominant contributor to the OMAT evolution of lunar regolith is the solar wind particles.