The spectral properties of Ca 4pnd(J = 3) autoionizing states have been studied by employing the combination of multichannel quantum defect theory (MQDT) with the K -matrix method. The cross section of 4p 3/2 15d excited from 4s15d and energy levels of 4pnd (J = 3) are calculated by using a theoretical model with more complete channels, and the configuration interaction is analysed in detail between 4p 1/2 nd, 4p 3/2 nd 3/2,5/2 and 4p 1/2,3/2 ng of five Rydberg series.