Objective To evaluate the influence of family members’ synchronous instruction education on uncertainty in illness among patients with postoperative limb lymphedema(PLL) treated with complex decongestion therapy(CDT). Methods From February 2018 to March 2018, convenience sampling was adopted to investigate 60 patients with PLL treated with CDT. The 60 patients were divided into control group and experimental group averagely and randomly. The 30 patients in the control group received routine health education, and the patients in the experimental group received routine health education and synchronous instruction for family members together. The patients in the two groups were investigated by Mishel disease uncertainty scale(Chinese version) before CDT treatment and after one course of CDT treatment. Results Before the first CDT treatment, the disease uncertainty scores of the control group and the experimental group were(70.60 ±4.78) and(69.67±3.72),respectively, with no significant difference between the two groups(P>0.05); after one course of CDT treatment, the disease uncertainty scores of the control group and the experimental group were(67.10 ±3.19) and(59.40±2.28), respectively, with statistical difference. Significance(P<0.05). Conclusion The uncertainty in illness for the PLL patients treated with CDT can be effectively reduced by the combination of routine health education and synchronous instruction for family members.