设置大小 sg.Canvas 符合 Matplotlib ，您最好指定一个选项 figsize 及 dpi ，则可以得到大小为（figsize[0]*dpi，figsize[1]*dpi）。
方法 sg.pin 就是保持 sg.Canvas 当看不见的时候。 window['-CANVAS-'].Widget.pack() 就是让它在任何时候都可见 update 方法 sg.Canvas .
方法 contents_changed 调用以更新的滚动条 sg.column 在这里 window.refresh() 需要在更新之前更新gui。

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
import PySimpleGUI as sg
import matplotlib
matplotlib.use('TkAgg')

def draw_figure(canvas, figure):
    figure_canvas_agg = FigureCanvasTkAgg(figure, canvas)
    figure_canvas_agg.draw()
    figure_canvas_agg.get_tk_widget().pack(side='top', fill='both', expand=1)
    return figure_canvas_agg

column = [
    [sg.Button("Load CSVs", key="-loadcsv-")],
    [sg.pin(sg.Canvas(size=(500, 500), visible=False, key='-CANVAS2-')),
     sg.InputText(size=(10,1), key="threshold"),
     sg.Button("Set Threshold", key="-threshold-")],
    [sg.InputText(size=(50, 1), key='-MODELNAME-'),
     sg.FileBrowse("Load Model")],
]
layout = [[sg.Column(column, vertical_scroll_only=True, scrollable=True, size=(800, 400), key='-COLUMN-')]]
window = sg.Window('Demo Application - Embedding Matplotlib In PySimpleGUI', layout, finalize=True, element_justification='center', font='Helvetica 18')
fig_canvas_agg = None

while True:
    event, values = window.read()
    if event == sg.WINDOW_CLOSED:
        break
    elif event == "-threshold-":
        if fig_canvas_agg is None:
            fig = matplotlib.figure.Figure(figsize=(5, 4), dpi=100)
            t = np.arange(0, 3, .01)
            fig.add_subplot(111).plot(t, 2 * np.sin(2 * np.pi * t))
            fig_canvas_agg = draw_figure(window['-CANVAS2-'].TKCanvas, fig)
            window['-CANVAS2-'].Widget.pack()
            window.refresh()
            window['-COLUMN-'].contents_changed()

window.close()