The invention discloses an agent for classifying leukocyte, comprising: a, at least two cationic surface active agents; b, at least one organic compound with hydrophobic group and anion group; c, a buffer agent for adjusting pH value at 2 to 8. The invention discloses a method for classifying leukocyte via the agent. The agent and method can quickly dissolve red blood cells and classify leukocytes into five types via one channel, while the reaction is processed under 10 to 40 DEG C, and the leukocytes can be classified into five types via detecting the scattered light signals of two angles.