The paper calculates the tide factor and phase lag by using Venedikov harmonic analysis of Cave Strain Observation of the Zhangjiakou-Bohai seismic belt, and the stability of the tide factor as the evaluation index. The paper then discusses the calculation models and usability of three orientation and two orientation strain parameters based on Huailai station, and the conclusion shows that the correlation coefficient of two calculation models results is above 0.9. We calculate the strain parameters time sequence of 16 stations on the Zhangjiakou-Bohai seismic belt with the calculation model of strain parameters, and we summarize the significant trend reverse of the strain parameters on the several earthquakes （ML ≥ 5.0） of North China. Finally we contrast the cave strain and GPS strain, and discuss the possible reasons of the difference.