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• The flammability limits and burning velocities of R1234yf mixtures were measured. • The relationship between flammability limit ranges and the n F /n H was analyzed. • The factors affecting the burning velocity were explored in the molecular structure. In response to the pressure of environmental protection, a series of environment-hazardous refrigerants will be phased out. And the selection of the substitutions for the future will need to balance thermodynamic property, safety and sustainability. Thus, the mixed refrigerants are receiving increasing attentions for their special performances. In this paper, the flammability characteristics of the commonly used mixtures R32/R1234yf and R152a/R1234yf were experimentally researched. The flammability limits of the two binary mixtures at different proportions of R1234yf were measured in a 12L spherical glass vessel. And the burning velocities of the two mixtures at different equivalence ratios were measured in a cylindrical quartz vertical tube. It can be found that the flammability limit curves of R32/R1234yf were different from that of R152a/R1234yf. The ratio of F atoms to H atoms (n F /n H) for the two mixtures had a close relationship with the flammability limit ranges. The maximum burning velocity for R32/R1234yf and R152a/R1234yf tended to decrease with the increase of the R1234yf proportion, and also decreased with the increasing of the n F /n H. But the n F /n H was not the only impact on the burning velocity. The number of C–H bonds and the molecular structure reflected in the heat of combustion would be correlated with the burning velocities of the mixtures. The results will provide a guidance for the development and safe application of R1234yf mixtures. [ABSTRACT FROM AUTHOR]