The invention provides a method for directly measuring specimen strain in a medium environment. The method comprises the following steps: a) carrying out redesign on a specimen; b) measuring the distance between two bosses, and fixedly arranging the specimen on a traction apparatus; c) clamping and fixing one end of each guidance clamp to the corresponding boss, and connecting the other end of the guidance clamp to a rigid guidance rod and enabling the guidance rod to be parallel to the specimen, and inserting each guidance rod into a displacement sensor, wherein the insertion portion is within the measurement range of the displacement sensor; d) placing the specimen in the medium environment, starting the traction apparatus to carry out traction on the specimen, recording the measurement values of the displacement sensors; and e) calculating the strain value of the specimen. Therefore, through the bosses, the part needing measuring can be measured directly; and compared with an indirect measurement method, the measurement method is more direct and higher in data measurement precision.