The invention discloses a movable on-site grouting machine for outer wall insulation boards, which is provided with a rectangular chassis, the rectangular chassis is of a framework structure, the two long borders of the chassis are supporting guide rails, a grout bin is arranged on the chassis, the bottom of the grout bin is provided with guide rail sliders matched with the guide rails, a flashboard and a flashboard-opening handle are respectively arranged inside and outside the grout bin, a grout scraper is obliquely connected with the lower part of the outer side of the grout bin, and a supporting frame for an outer wall insulation board is arranged in the cavity right under the chassis. By means of a handrail and truckles, the on-site grouting machine can be flexibly moved to any construction site, and the size is small. The semi-automation of on-site grouting operation is realized, the labor intensity is reduced, and the working efficiency and the grouting quality are increased.