1. If the position is large, the risk borne will increase accordingly, and the margin given by brokers to customers will also be required to increase.

2. Keep this position for a long time. If the price is not conducive to your speculative direction, and you don't close your position in time, you will be asked by the brokerage firm to increase the margin.

3. If the price of the variety of positions fluctuates greatly, it will also be required to increase the margin.