This paper attempts to find a new conformity index (CI) calculation method with slice and angle information for evaluating lung cancer radiation treatment plan. A total of 20 lung cancer patients in 2016–2019 were selected. Treatment plans were made for each patient. Parameters used in the process of making treatment plans were set the same. The CI and the standard-deviation based CI (SDCI) that contains angle and slice information were calculated. Comparison of results calculated with SDCI and CI were made. The results of the two methods for the patients showed the same trend. Different shapes of simulated dose distribution line shows SDCI can provide more detail information about the target area. Special shapes of simulated dose distribution line for SDCI showed inaccuracy in angle information. The parameter SDCI has more advantage towards the traditional CI for it can provide angle and slice information. However, more angles need to be calculated.