The ambient temperature variation and drying shrinkage of concrete experienced by ultra-long isolated structures have certain regional and random characteristics. The probability method is used to study the unit division method of ultra-long isolated structures during the construction period to effectively control the thermal shrinkage deformation of the isolation layer. Firstly， the unit division mechanism of ultra-long isolated structures during the construction period is studied， and the control method of the thermal shrinkage deformation of the isolation layer is proposed. Secondly， based on the generalized extreme value distribution model， the optimal distribution model parameters of mean minimum temperature of the coldest month， mean temperature of the hottest month and annual average relative humidity in 12 high-intensity cities with different ambient temperature and humidity distributions are calculated. Combined with the three ambient temperature and humidity levels proposed for the construction period of ultra-long isolated structures， the recommended values of comprehensive temperature difference in 12 cities under different levels is given. Furthermore， the calculation method of the maximum setting spacing of the post-pouring belt is proposed. Then， the unit division method of ultra-long isolated structures during the construction period is summarized. Finally， the optimization analysis of unit division scheme of an ultra-long isolated structure under construction is carried out. The results show that under the condition that the stiffness generation time of the isolation layer is constant and the concrete dry shrinkage mode is determined， to ensure that the maximum thermal shrinkage deformation of the isolation layer in the synthetic direction is controlled within the limit of 55 mm， the temperature of the isolation layer in the coldest month needs to be raised to -4 °C and above when the post-pouring belt division scheme 3 and the closed scheme 1 can be adopted. To ensure the integrity of the structure and the convenience of construction， the post-pouring belt division scheme 2 and the closed scheme 1 can be adopted， and the temperature of the isolation layer in the coldest month needs to reach -1 °C and above.