The invention provides a computer system used in determination of recurrence risk of colorectal cancer. The computer system is provided with a computer including a processor and a storage. The storage is recorded with a computer program which is executed in the computer. The method comprises receiving expression quantity of a plurality of genes selected by a first gene group existed in a region of 18q21 to 18q23 on an eighteenth chromosome long chain in a live sample acquired from a colorectal cancer patient, receiving expression quantity of a plurality of genes selected by a second gene group existed in a region of 20q11 to 20q13 on an twentieth chromosome long chain in a live sample acquired from a colorectal cancer patient, and receiving expression quantity of a plurality of genes selected by a third gene group including ANGPTL2, AXL, C1R, C1S, CALHM2, CTSK, DCN, EMP3, GREM1, ITGAV, KLHL5, MMP2, RAB34, SELM, SRGAP2P1, and VIM in a live sample acquired from a colorectal cancer patient, and based on the received expression quantity, determining recurrence risk of colorectal cancer for the patient.