The technique of fatigue tests of steel cross-shaped samples with a surface crack under biaxial loading is described. The sample and equipment for the implementation a biaxial tension and compression-tension in a working part of the sample are proposed. The sample and equipment for the implementation a biaxial tension and compression-tension in a working part of the sample are offered. Test results of structural steel 20 samples are presented. A stress effect parallel to a crack plane on its growth rate is determined. Crack tip plastic zone shape and sizes under various loading conditions are studied. The relationship of a fatigue crack growth rate and a plastic deformation area size is established. The formula to determine the growth rate of a surface crack under biaxial loading taking into account a plastic deformation is proposed.