Solution of: https://stackoverflow.com/questions/46461619/how-to-put-a-groupbox-inside-a-gridlayout-pyqt4

main.py

import sys

from PyQt4.QtCore import *
from PyQt4.QtGui import *


class Widget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setLayout(QGridLayout())
        for i in range(20):
            letter = chr(ord('a') + i)
            checkBox = QCheckBox('{}'.format(i+1), self)
            self.layout().addWidget(checkBox, i, 0)

            btna = QPushButton("{}1".format(letter), self)
            btnb = QPushButton("{}2".format(letter), self) 

            self.layout().addWidget(btna, i, 1)
            self.layout().addWidget(btnb, i, 2)


class Tab1(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setLayout(QGridLayout())

        self.group = Widget(self)
        scroll = QScrollArea(self)
        scroll.setWidget(self.group)
        scroll.setWidgetResizable(True)

        self.layout().addWidget(scroll)
        self.runBtn = QPushButton("Run", self)
        self.layout().addWidget(self.runBtn)


class Page1(QTabWidget):
    def __init__(self, parent=None):
        super(Page1, self).__init__(parent)
        self.tab1 = Tab1()
        self.tab2 = QWidget()
        self.tab3 = QWidget()
        self.addTab(self.tab1, "Tab1")
        self.addTab(self.tab2, "Tab2")
        self.addTab(self.tab3, "Tab3")
        self.tab2_initUI()
        self.tab3_initUI()

    def tab2_initUI(self):
        grid = QGridLayout()
        self.tab2.setLayout(grid)

    def tab3_initUI(self):
        grid = QGridLayout()
        self.tab3.setLayout(grid)

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setGeometry(300, 200, 600, 370)
        self.startPage1()

    def startPage1(self):
        x = Page1(self)
        self.setWindowTitle("Auto Benchmark")
        self.setCentralWidget(x)
        self.show()

def main():
    app = QApplication(sys.argv)
    main = MainWindow()
    main.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()