The invention discloses a construction method of a rectangular ultra-shallow covered soil tunnel. The method comprises the steps that before a tunnel is excavated, one row of cast-in place piles are arranged on two sides of a tunnel side boundary in the tunnel axial direction in the crossing range of ultra-shallow covered soil respectively; high pressure jet grouting piles are arranged in a reinforcing area defined by the two rows of cast-in place piles and the top of the tunnel; concrete anti-floating plates are casted at the tops of the cast-in place piles and the high pressure jet grouting piles. Anti-floating strengthening construction is performed before, when and after a rectangular shield crosses the ultra-shallow covered soil respectively, compared with a conventional measure that only anti-floating is performed when the rectangular shield crosses the ultra-shallow covered soil, the construction method of the rectangular ultra-shallow covered soil tunnel has better anti-floating strengthening strength and can solve the difficulties that tunnel floating is large, ground disturbance is fierce, and the shield posture is difficult to control under the rectangular shield ultra-shallow covered soil condition.