The invention discloses a device and a method for detecting total cyanide and sulfide in a water solution by employing direct conversion. The method comprises the following steps: feeding a sample solution of which the pH is greater than or equal to 11 into a six-way valve quantitative loop to quantify through an online filter, feeding excessive sample solution into a liquid waste bottle; switching a six-way valve, pumping a pure water solvent as a carrying current, pushing out the sample solution, and pumping a water solution containing a stabilizer and an exchanger in advance; after mixing with the sample coming from quantitative loop samples, switching a three-way valve, and refluxing into a storage bottle, further pushing the solution to be mixed evenly in a mixing pipe by virtue of the pure water solvent; entering a photolysis device to carry out photolysis until reaching a capture column in the six-way valve in an ion chromatograph; locking a to-be-detected object, feeding a non-to-be-detected object into the liquid waste bottle; rising the capture column by using an eluting solution, and entering a separation post; sequentially discharging the sulfide and cyanide; and respectively detecting the sulfide and the cyanide by virtue of an ampere detector, and then rinsing the separation column in a reinforcing manner. Compared with an existing national standard method, the method disclosed by the invention is green, safe, environment-friendly, and little in interference; the analysis time, the laboratory safety and the cost are obviously improved; and use of a toxic reagent is also reduced.