如果你是用Anaconda的話，開啟cmd或Anaconda Prompt，直接在你想要的環境中輸入
conda install pyqt5

如果你使用原生python則可以輸入pip指令安裝
pip install pyqt5

下載Qt Designer

先下載Qt的Qt Designer製作工具，有許多現成的元件可以圖像化製作，在軟體中拉一拉元件，規劃你要的介面，就可以直接輸出.ui檔

使用pyuic5工具

可以將.ui檔轉換為.py檔供python使用，為安裝PyQt5後附加的工具，於cmd中切換到當前環境目錄(例:...\Anaconda3\Scripts\pyuic5.exe)，輸入語法為
pyuic ui_file_from_QtDesigner.ui -o ui_file_for_python.py
Where is pyside-uic.exe? https://stackoverflow.com/questions/6684180/where-is-pyside-uic

下列附上ui介面完整程式碼:

# -*- coding: utf-8 -*-
# Created by: PyQt5 UI code generator 5.9.2
# WARNING! All changes made in this file will be lost!
from PyQt5 import QtCore, QtGui, QtWidgets
import sys
class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName("Form")
        Form.resize(600, 800)
        self.gridLayout = QtWidgets.QGridLayout(Form)
        self.gridLayout.setSpacing(10)
        self.gridLayout.setObjectName("gridLayout")
        self.label = QtWidgets.QLabel(Form)
        self.label.setObjectName("label")
        self.gridLayout.addWidget(self.label, 0, 0, 1, 1)
        self.comboBox = QtWidgets.QComboBox(Form)
        self.comboBox.setObjectName("comboBox")
        self.gridLayout.addWidget(self.comboBox, 1, 0, 1, 2)
        self.pushButton = QtWidgets.QPushButton(Form)
        sizePolicy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Fixed, QtWidgets.QSizePolicy.Fixed)
        sizePolicy.setHorizontalStretch(0)
        sizePolicy.setVerticalStretch(0)
        sizePolicy.setHeightForWidth(self.pushButton.sizePolicy().hasHeightForWidth())
        self.pushButton.setSizePolicy(sizePolicy)
        self.pushButton.setObjectName("pushButton")
        self.gridLayout.addWidget(self.pushButton, 1, 2, 1, 1)
        self.label_2 = QtWidgets.QLabel(Form)
        self.label_2.setObjectName("label_2")
        self.gridLayout.addWidget(self.label_2, 2, 0, 1, 1)
        self.comboBox_2 = QtWidgets.QComboBox(Form)
        self.comboBox_2.setObjectName("comboBox_2")
        self.gridLayout.addWidget(self.comboBox_2, 3, 0, 1, 1)
        self.lineEdit = QtWidgets.QLineEdit(Form)
        self.lineEdit.setObjectName("lineEdit")
        self.gridLayout.addWidget(self.lineEdit, 3, 1, 1, 2)
        self.listWidget = QtWidgets.QListWidget(Form)
        self.listWidget.setObjectName("listWidget")
        self.gridLayout.addWidget(self.listWidget, 4, 0, 1, 3)
        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)
    def retranslateUi(self, Form):
        _translate = QtCore.QCoreApplication.translate
        Form.setWindowTitle(_translate("Form", "爬蟲工具"))
        self.label.setText(_translate("Form", "看板"))
        self.pushButton.setText(_translate("Form", "+"))
        self.label_2.setText(_translate("Form", "關鍵字搜尋"))
if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    window = QtWidgets.QDialog()
    ui = Ui_Form()
    ui.setupUi(window)
    window.show()
    sys.exit(app.exec_())
執行後畫面長這樣:

Reference
Using Qt Designer

https://www.riverbankcomputing.com/static/Docs/PyQt5/designer.html