Is it correct to say “I’m a 400l student of Animal science department, faculty of agriculture in university of Port Harcourt?” Or can it be rephrased?

Your sentence is understandable, but it can be rephrased for clarity and correctness. Here’s a more polished version: "I am a 400-level student in the Department of Animal Science, Faculty of Agriculture, at the University of Port Harcourt." This version uses "400-level" instead of "400l" for clarity and corrects the structure slightly.