  In this paper, we present statistics of soft gamma repeater (SGR) bursts from
SGR J1550-5418, SGR 1806-20 and SGR 1900+14 by adding new bursts from
K{\i}rm{\i}z{\i}bayrak et al. (2017) detected with the Rossi X-ray Timing
Explorer (RXTE). We find that the fluence distributions of magnetar bursts are
well described by power-law functions with indices 1.84, 1.68, and 1.65 for SGR
J1550-5418, SGR 1806-20 and SGR 1900+14, respectively. The duration
distributions of magnetar bursts also show power-law forms. Meanwhile, the
waiting time distribution can be described by a non-stationary Poisson process
with an exponentially growing occurrence rate. These distributive features
indicate that magnetar bursts can be regarded as a self-organizing critical
process. We also compare these distributions with the repeating FRB 121102. The
statistical properties of repeating FRB 121102 are similar with magentar
bursts, combing with the large required magnetic filed ($B\geq 10^{14}$G) of
neutron star for FRB 121102, which indicates that the central engine of FRB
121102 may be a magnetar.
