Aiming at the problems, which are too much alkalinity in chromogenic agent and standard solution and no coloration, in “isonicotinic acid sodium-barbituric acid sodium spectrophotometric method for hydrogen cyanide and cyanide in the air of workplace”, the preparation of chromogenic agent and dilution method of standard solution were improved. After improvement, chromogenic reaction is significantly sensitive and linearity of the calibration curve is good. The actual samples testing proved that test results are accurate and the method is feasible.