The invention relates to a fry breeding method of tetraploid fry of brachymystax lenok. The method comprises the following steps of firstly, performing in-vitro fertilization on eggs and sperms of parent brachymystax lenok; then, treating the fertilized eggs by means of a heat shock method; then, carrying out temperature change treatment on the fertilized eggs; finally, incubating the fertilized eggs in water for breeding, and performing culturing to obtain the tetraploid fry of brachymystax lenok. According to the method, the preparation of the tetraploid fry of brachymystax lenok is realizedby adopting an in-vitro fertilization technology for female and male brachymystax lenok and the heat shock method, the eyed rate, fry hatchability rate and tetraploid rate of the fertilized eggs areeffectively increased, and a stable triploid brachymystax lenok population can be obtained through hybridization with normal diploid brachymystax lenok, so that the problems of sexual prematurity, individual miniaturization and the like of bred individuals, which are caused by long-term inbreeding and lack of systematic breeding in a brachymystax lenok breeding process, are solved. The method increases the specification and growth speed of commercial fishes obtained through brachymystax lenok breeding and production and has good economic benefits and a high market value.