The current in the capillary can affect the state of the plasma in pinch process and affect the soft X-ray laser. The inductance of the main switch can change the current waveform. Therefore the scheme of changing current waveform is put forward with different main switches to find the best current waveforms, which are fit for soft X-ray pumped by capillary discharge. In the experiment, three kinds of main switches are used to observe the effect of inductance on the current duration and amplitude. The inductance of main switch is estimated and the current amplitude and duration are calculated with pulse power theory. The theoretical results are compared with the experimental data. With three different main-switches, the influence of current waveforms on soft X-ray laser spike is observed. The experimental results show that the ring-disk-shaped main switch, discharge distance of which is 3 cm, is fit for soft X-ray laser best.