In view of the situation that the kinetic model which is necessary for the traditional time temperature indicator (TTI) selection method is complex and inaccurate for the multiple regressions, a convenient and intuitive method based on the contour lines was proposed. The method is demonstrated in theory, and analyzed with the traditional method through an experiment about Muscat Hamburg grape and four kinds of TTI. The result shows that the TTI of Vitsab M25-2 could be considered as the best candidate to monitor firmness losses of Muscat Hamburg, and this is similar to the result from the traditional kinetic model. Meanwhile, the differences of the contour lines between the grape and TTIs are positive correlated with the differences between the activation energy of them, which confirms the reliability of the TTI selection method based on contour lines.