The equation of the twinphoton circles produced in nonlinear optical type-Ⅱ spontaneous parametric down conversion(SPDC) was derived.The change of image of the conjugate circles was analyzed. The interesting featuresarising from the form of the two-photon state generated in the process were discussed. Thegeometric optics phenomena of the rings of radiation from the crystal were described. Thegeneration condition of high-efficiency beamlike twin photon was demonstrated.