The classical 1-D vertical advection-diffusion model was improved in this work. The main advantages of the improved model over the previous one are: 1) The applicable condition of the 1-D model is made clear in the improved model, in that it is substantively applicable only to a vertical domain on which two end-member water masses are mixing. 2) The substitution of parameter f(z) in the equation of the classical 1-D model with end-member fraction f 1z makes the model more precisely and easily solved. 3) All the terms in the improved model equation have specific physical meanings, which makes the model easily understood. Practical application of the improved model to predict the vertical profiles of dissolved oxygen and micronutrients in abyssal ocean water of the North Pacific proved that the improvement of the 1-D advection-diffusion model is successful and practicable. The classical 1-D vertical advection-diffusion model was improved in this work. The main advantages of the improved model over the previous one are: 1) The applicable condition of the 1-D model is made clear in the improved model, in that 2) The substitution of parameter  f (z)  in the equation of the classical 1-D model with end-member fraction  f 1z  makes the model more precisely and easily solved. 3) All the terms in the improved model equation have specific physical meanings, which makes the model easily understood. Practical application of the improved model to predict the vertical profiles of dissolved oxygen and micronutrients in abyssal ocean water of the North Pacific proved that the improvement of the 1-D advection-diffusion model is successful and practicable.