Herein, an innovative sandwich-type electrochemical immunosensor based on multi-order Rubik's cube-type platinum nickel nanocubes and Au NPs/cPDA NTs was used for the ultrasensitive detection of carcinoembryonic antigen (CEA). In this process, an appropriate amount of uniformly dispersed gold nanoparticles (Au NPs) was effectively immobilized on nitrogen riched carbonized polydopamine nanotubes (cPDA NTs) through Au-N bonds, avoiding the stacking and agglomeration of Au NPs, thereby enhancing the conductivity. Subsequently, multi-order Rubik's cube-type platinum nickel nanocubes (PtNi NCs), composed of numerous small interlaced nanocubes, was successfully prepared to immobilize the secondary antibodies (Ab) effectively. Due to its inherent hierarchical architectures and high density of active sites, PtNi NCs exhibited excellent mass and electron transfer performance towards the reduction of hydrogen peroxide (HO) for amplifying the current signal to detect CEA. The rationally designed immunosensor presented a broad linear ranging from 50 fg mL to 100 ng mL and a low limit of detection of 17.78 fg mL (S/N = 3) for CEA determination under optimal conditions. Furthermore, the as-fabricated immunosensor exhibited excellent selectivity, reproducibility and stability, which can be extended to accurate and sensitive detection of other biomarkers.