A counter-pressure casting method for an aluminum alloy shell for an armored vehicle water propulsion device comprises the steps of a, material preparation; b, alloy smelting; c, mold assembly; d, counter-pressure casting; e, heat treatment; and f, mechanical machining. Compared with ordinary sand casting and conventional low-pressure casting aluminum alloy shells, the aluminum alloy shell, manufactured by the counter-pressure casting method, for the armored vehicle water propulsion device has the following advantages that (1) the aluminum alloy shell, manufactured by the counter-pressure casting method, for the armored vehicle water propulsion device is subjected to X-light and ultrasonic wave detection, the internal structure is compact, and casting defects like slag inclusion, looseness, shrinkage cavities, air pores and cracks are avoided; (2) the mechanical property is remarkably improved, the tensile strength Rm is improved by 10-20% to reach 450-480 MPa, and the percentage elongation after fracture A is improved by 30-50% to reach 8.0-12.0%; and (3) the casting qualification rate is remarkably improved and reaches 96% or above.