Simply put, the principle of the greenhouse is heat absorption and heat preservation. On the one hand, the covering material of the greenhouse can absorb light and heat, on the other hand it can also keep warm and prevent the heat from lossing.
After the short wave radiation of the solar radiation enters the greenhouse through light-absorbing material, the short wave radiation will be converted into long wave radiation. and the ground temperature and interior temperature will rise. And the long-wave radiation is blocked in the greenhouse by the greenhouse covering material. The heat in the greenhouse will be accumulated. This process is called the "greenhouse effect".
People take advantage of greenhouse effect to achieve the purpose of crop anti-season production and the increasing yield of the crop by increasing the indoor temperature in a cold season where the crop is not suitable for outdoor growth to create a suitable environment for crop.