| Let △（2）mn denote a type-II triangulation of a rectangular D := [a,b](?)[c,d]and denote the spaces of cubic spline with boundary condition:In this paperi we shall discuss the existence and uniqueness of a certain class of in-terpolation by S1，13（△（2）mn）, and estimate their approximation degree: For f ∈C4(D),then ｜ｆ－ｓ｜≤ｋ（ｌ）·ｍａｘ（ρ△，ρ－１△）·‖ｆ‖．·ｈ2． |
