This research reports the simultaneous multi-analyte sensing capabilities of a D-shaped multi-channel surface plasmon resonance (SPR) sensor. Three channels are truncated in a U-shaped pattern at the side-polished surface of the D-shaped three-core fiber. Three Gold-nanowires (AuNWs) are positioned at the bottom of each sensing channel. To examine the SPR sensor's multi-channel characteristics, a finite element method (FEM) is applied. In order to detect a variety of analytes, y-polarized modes-multiplexing is used, which offers a sufficient wavelength range. At an infiltrated refractive index (RI) of 1.35, 1.38, and 1.41, respectively, the maximal RI sensitivities of c-1 (channel-one), c-2 (channel-two), and c-3 (channel-three) are found as 7,611 nm/RIU, 5,128 nm/RIU, and 12,974 nm/RIU, respectively. Moreover, the sensing structure with three external sensing channels is being demonstrated first time, to the best of our knowledge, using multicore fiber for the detection and discrimination of three different analytes simultaneously. According to expectations, the proposed sensor may be helpful for the detection of a wide range of chemicals and bio-analytes.