Study aim: Determining the effect of mindfulness-based training on pain intensity and situational anxiety control of patients undergoing knee joint replacement surgery Design: A clinical trial study with two intervention and control groups -randomized - on 76 patients Settings and conduct: This study includes patients waiting for knee joint replacement surgery in Hefdeh Shahrivar and Imam Khomeini hospitals in Amol. First in the office, Spielberger, Pittsburgh, and McGill questionnaires are given to the intervention and control groups. During two thirty-minute sessions, which the first session is before hospitalization in the office and the second session is on the day of hospitalization, the four mindfulness techniques are taught to the intervention group. It was decided by nursing office that each group should be hospitalized in two departments of orthopedics and its support department ENT, so that there is no interference and communication between them, and at the same time they receive the same care .After the first session, the audio file of the training will be given to the patient for practice, and during the hospitalization after surgery, the patients questions will be answered. On the morning of the surgery, the Spielberger questionnaire is completed again by both groups. On the second, third, and fourteenth day after surgery, McGill and Pittsburgh questionnaires are completed by both groups. Participants/Inclusion and exclusion criteria: Inclusion criteria: candidates for unilateral joint replacement surgery Exclusion criteria: Any event that leads to the removal of the sample from the action list Intervention groups: Four mindfulness techniques which include: focus on breathing - body scan - visualization - mental stretching are taught to the intervention group and the control group receives training and routine care. Main outcome variables: anxiety; pain