The invention discloses a stirring tank emptying and slurry output concentration maintaining method based on tensioning dynamics. The method includes: step 1, acquiring parameters of a stirring tank and current and expected stirring tank output slurry concentration Cbd, Cbd=Cb (0), and setting an expected track hd (t) when liquid level height of the stirring tank is lowered to be zero at the same time, wherein the parameters include concentration Cb1 and Cb2 used for emptying two liquids of the stirring tank, and Cb1 is not equal to Cb2; step 2, utilizing a tensioning dynamics method to be combined with a stirring tank system equation to acquire a controller set; step 3, setting flowing speed w1 (t) and w2 (t) used for emptying the liquids of the stirring tank according to a controller group equation to enable stirring tank output slurry concentration Cb (t) to be quickly maintained to be current and expected stirring tank output slurry concentration Cbd and enable stirring tank liquid level lowering height h (t) to quickly converge to be the expected track hd (t) when the stirring tank liquid level height is lowered to be zero to achieve the objective of emptying the stirring tank. By the method, expected solvent can be prepared in a retaining manner to reduce industrial waste.