The Wide Field of View Cherenkov Telescope Array (WFCTA), a main component of the Large High Altitude Air Shower Observatory (LHAASO),
requires the dynamic range from 10 to 32000 photoelectrons (pes) and the stable gain for the photosensors.
Silicon photomultipliers (SiPMs) are new type of photosensors with respect to photomultiplier tubes (PMTs),
the performance of which is improved rapidly since 1990s.
SiPM do not suffer any ageing even with strong light exposure
and the SiPM-based cameras could operate with high moonlight and their duty cycle is much larger than that of PMT-based cameras.
In this paper, the design of preamplifier for the WFCTA camera is described.
The dynamic range of SiPMs is studied, especially the non-linearity while the number of photons is large.
A function is derived to describe the relationship between the number of fired cells and the total number of cells in the SiPM.
The linearity of SiPMs follows the function well and could be corrected by the function.
We also compared the performance of the SiPM and PMT under long time duration light pulses up to $3~\mu s$,
in order to investigate the stability of the gain of SiPMs.
Moreover, the additional nonlinearities due to the nonuniform light distribution and the misestimation of the gain are also evaluated.