The petawatt laser-driven proton accelerator at Peking University develops a laser proton radiotherapy system in response to the needs of proton radiation tumor treatment. The common collection section of its horizontal and vertical beam lines mainly consists of three superconducting solenoids (S₁-S₃). Large stresses are generated in the solenoids during the cooling down and excitation process, in addition, the superconducting solenoids are operated by fast ramping, and the AC loss in the process will have an important impact on the solenoid excitation speed and stable operation. In this paper, the highest field strength and the most complex structure of 7.8 T-120 mm solenoid S1 is taken as the research object, COMSOL Multiphysics software is used to carry out the stress analysis of superconducting solenoids under multi-field conditions, and at the same time, the simulation of the AC loss due to the rapid change of the current is carried out. The corresponding experimental studies were carried out to obtain the variation curves of strain with temperature, correlations between current, magnetic field and strain correspondingly. According to the experiment data, there is a significant positive correlation between the measured values of the magnetic field, the strain and the change of current, which verifies the rationality of the superconducting solenoid design. This study provides experience and reference for the subsequent design and development of similar superconducting magnets.