Hello @nghia1991ad,
Welcome to the GMT forum 
!
It sounds like you need the GMT flags -Fa, -Fe, -Fg, -Ft, -Fg. Unfortunately, there are no aliases for these flags in PyGMT available yet. But as a workaround, it is possible to use the flags directly in PyGMT (without the hyphen -) as parameters.
import pygmt
import numpy as np
size = 5
fig = pygmt.Figure()
fig.basemap(region=[-size, size] * 2, projection=f"X{size * 2}c", frame=0)
fig.meca(
spec=np.array([0, 0, 0, 35, 42, 70, 5]), # lon, lat, dep, strike, dip, rake, magnitude
scale="4c+m",
convention="aki",
Fa="0.5c/cd", # Compute and plot P and T axes with symbols, Adjust size and symbols
Fe="pink", # Adjust fill of T axis symbol
Fg="cyan", # Adjust fill of P axis symbol
Ft="2p,red", # Adjust outline of T axis symbol
Fp="2p,blue", # Adjust outline of P axis symbol
)
fig.show()
