The aplanatic parametric equation,that describes the one-one correspondence relation of ray parameter and coordinator,is established with the aperture height of the incident light as the variant,based on the aplanatic principle and ray tracing method. The intersecting line of aspheric meridional ray presented by the equation is a continuous real curve since the parameter is also a continuous real variable. The rotating surface of the intersecting line is an aplanatic refraction surface. Meridional intersecting line is a high-order curve of the aperture height. The parametric quadratic equation in two variables refers to the convergent emergent rays and in one variable refers to the parallel emergent rays. Without analytic hyperbolic curve or high-order correction item,this parametric equation can realize zero spherical aberration design for the curves with multi-turning points,such as long focal distance system,large aperture system and Schmidt corrector.