In this paper, we use diffractive superresolution technology to design a pure-phase plate for realizing the smaller spot size than the usual Airy spot size. We have calculated 2,3,4,5 circulation zones for optimizing the highest energy compression (Strelratio) with the constraint of the Firstzero value G=0.8. Numerical results show that the 2-circular zone pure-phase plate can yield the highest Strelratio (S=0.59) with the constraint of G=0.8.The 3-circular zone pure-phase plate with the respective phases of φ1φ2φ3 has also been calculated. At the same time the 4,5 circular zone binary phase (0,π) plates are calculated to yield the result of S = 0.57 with G=0.8. The usage of the superresolution phase plate aims to realize the smaller spot size instead of the usage of the higher numerical aperture lens, which is the main advantage of this superresolution technology. Therefore, in this constraint of G=0.8, we have selected the 2-circular zone with binary phase for ease of fabrication. At last, we use a 50 nanometer fiber tip detector to scan the diffractive superresolution light spot in order to compare it with the Airy spot. Detailed experiments are presented.