The objective of this study was to determine the effects of horticultural therapy (HT) program based on the self-expression model for improving adjustment to military life of soldiers in military service. A total of 60 soldiers in air force located in Gyeonggi province, South Korea were participated in this study. Soldiers were randomly divided into experimental group (n=30) and control group (n=30). A HT program that consisted of a 10-session was developed for this study and was conducted from August to October of 2014. The main activities in the HT program were planting, making crafts by using plants, and flower arrangement. Feeling expression that is a part of the self-expression model was separated by three stages such as intimacy and relationship formation stage, situational awareness and emotional expression stage, and strengthen inner insight (emotional overcome) and emotion defuse stage. Moreover, the selected relevant factors such as depression, anxiety, interpersonal relationships, etc. were applied to the each session for improvement adjustment to military life of soldiers. After finishing the HT program, anxiety, depression, ego-resilience, interpersonal relationships, and adjustment to military life showed a significant improvement in experimental group except the variable, stress to military life. In the control group, there was no significant difference in the six variables after the HT program. The participants in the experimental group reported a high level of satisfaction for the HT program in the satisfaction survey. In conclusions, the HT program based on the self-expression model for improving adjustment to military life of soldiers showed significantly significant improvements. Additionally, it would be interesting to investigate the effects of HT program for improving adjustment to military life to cared soldier who is more serious problem in the military service.