The invention relates to a method for judging bicrystal alloy. The method for judging the bicrystal alloy comprises the following steps: preparing a metallographical phase of a to-be-tested alloy sample, and respectively measuring cross sectional areas S of multiple grains in the metallographical phase; ranking the obtained multiple cross sections S in an ascending sequence of grain serial number n in a small-to-large ranking manner to form a cross sectional area sequence Sn; calculating difference value delta S of two cross sectional areas with grain sequence number difference of constant k, wherein the interval constant k is a positive number; ranking the obtained multiple difference values delta S in an ascending sequence of the grain serial number to obtain a difference value sequence delta Sn; obtaining a numerical value hopping region in the difference value sequence delta Sn, wherein a grain serial number corresponding to a starting value in the numerical value hopping region is the characteristic grain number N; when ratio of quantity of grains with the grain serial numbers less than the characteristic grain serial number N to quantity of grains with the grain serial numbers more than or equal to the characteristic grain serial number N is (1-9):(9:1), judging the to-be-tested alloy sample to be the bicrystal alloy.